Table of Content

This page gives information on the numerous interfaces of the Atari ST and the associated connectors and cables. It also provides information on some standard cables and connectors not specific but useful for the Atari ST.

 

Important note: On this page the connectors pinout are always given looking at them from the front side and not from the solder side.

 

LOCATION OF THE INTERFACES CONNECTORS

 

 

On the left side you find connectors for the midi in and out, and a cartridge and the right underside contains the connectors for the Mouse & Joysticks

 

 

On the back panel you find connectors for a modem, printer, hard disks, floppy disk, TV (Atari with RF modulator) and monitor Back to the top

ATARI MIDI INTERFACE

The midi interface is used to connect the Atari to electronic musical instruments. It uses asynchronous signals (8 bits plus start and stop bits) at 31250 bauds (bit/sec). The Atari interfaces midi through a dedicated 6850 ACIA (Asynchronous Communication Interface Adapter) chip as shown on the right.

Note the unconventional connection of Midi Thru signals to pin 1 & 3 of the out midi connector. This allows to have a midi thru interface without the cost of an extra connector.

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Atari Midi Connectors

The Atari has two midi DIN5 connectors: A standard Midi In connector, and a non standard Midi Out connector that also includes the Midi thru output (this was done to avoid adding a third connector as specified in the standard midi)

1 THRU Transmit data (non standard)
2 Shield Ground
3 THRU Loop return (non standard)
4 OUT Transmit data
5 OUT Loop return
Midi Out/Thru Pinout DIN5 female
1 Non connected
2 Non connected
3 Non connected
4 IN Receive data
5 IN Loop return
Midi In Pinout DIN5 female

Note that a shield is connected on the Midi Out connector which is not following the midi standard. It is therefore recommanded to use cable without shield connection. For the Midi In connector there is no shield which is standard midi.

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Standard Midi Cables

It is possible to use standard Midi cables for the Midi In and the Midi Out connection to/from the Atari. However it is mandatory to check that the cable connected to the Atari Midi Out does not have any wires connected to pin 1 & 3. This should be the case if you use a "standard midi cable" as describe below, but sometimes you will find DIN5 male-male audio cables that connects all the pins.

 

DIN5 male

DIN5 male
Name DIN5 DIN5
Shield 2 2
Data 4 4
Loop return 5 5
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Atari Special Midi Out Midi Thru Cable

It is possible to build a special Y cable that allows to have a Midi Out port as well as a Midi Thru port coming from the Atari. For that matter you need to connect two cables on a male DIN5 connector (the one connected to the Atari Midi Out)  and each of them are terminate on a male DIN5 connector. The Y cable connections are described below. Here is a picture of this cable

 
DIN5 male
DIN5 male
DIN5 male
Name Atari Out DIN5 Midi Thru DIN5 Midi Out DIN5
Thru sink 1 4  
Shield 2 2 2
Thru source 3 5  
out sink 4   4
out source 5   5
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ATARI CARTRIDGE INTERFACE

This interface allows to use a ROM cartridge with a maximum size of 128KB. It connects the internal bus with the cartridge connector as described below.

Pin

  Name  

Pin

  Name
1   + 5 VDC   21   Address 8
2   + 5 VDC   22   Address 14
3   Data 14   23   Address 7
4   Data 15   24   Address 9
5   Data 12   25   Address 6
6   Data 13   26   Address 10
7   Data 10   27   Address 5
8   Data 11   28   Address 12
9   Data 8   29   Address 11
10   Data 9   30   Address 4
11   Data 6   31   ROM Select 3
12   Data 7   32   Address 3
13   Data 4   33   ROM Select 4
14   Data 5   34   Address 2
15   Data 2   35   Upper Data Strobe
16   Data 3   36   Address 1
17   Data 0   37   Lower Data Strobe
18   Data 1   38   Ground
19   Address 13   39   Ground
20   Address 15   40   Ground
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ATARI SERIAL INTERFACE

This interface is used generally for communication with other computers or with modems. Most of the connection comes from the USART (Universal Synchronous/Asynchronous Receiver/Transmitter) inside the MFP68901 with the exception of the DTR and RTS signals that comes from the I/O port of the sound chip.
The modem interface on Atari ST computers follows the RS232 standard apart from the following non-tested information: The CTS signal (that usually indicates that the modem is ready to take the next character) is connected to input I2 of the MFP68901 and generates an interrupts used by the system to start transmission. Therefore the CTS has to be pulsed (i.e. transitioned) for each character to send (in other word keeping it asserted does not work). As the RTS is pulsed for each character to send it can be directly connected to CTS.
Again this is information coming from "the Atari ST bible" book and I did not verified it?

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Serial Interface Connector

The serial interface uses a 25 pins D-SUB male Connector

Pin Name Description
   
1 SHIELD Shield Ground. should not be connected to Ground
2 TXD Transmit Data
3 RXD Receive Data
4 RTS Request to Send.
5 CTS Clear to Send
6 DSR Not Connected (Data Set Ready)
7 GND System Ground
8 CD Carrier Detect
9-19 N/C  
20 DTR Data Terminal Ready
21 N/C  
22 RI Ring Indicator
23-25 N/C  
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Serial Interface Cables

Connection to a modem uses a normal modem cable (e.g. DB25F-DB25M or DB25F-DB9M).
Connection to another computer (e.g. a PC) requires a null modem cable (e.g. DB25F-DB25F or DB25F-DB9F).

Plese refer to the RS232 Standard for description of these cables.

ATARI PARALLEL INTERFACE

 

The parallel interface also called the printer interface of the Atari is somewhat standard but is missing several standard signals found on PC's parallel interface (see description below).

The printer signals are connected mostly on the Yamaha sound chip I/O ports! The only exception is the Busy signal that goes to input I0 of the MFP68901, and therefore a transition on this pin generates an interrupt.

The other signals shown in the schematic on the right are used in the Audio/Video Interface (audio in and out) , in the floppy disc interface (drive 0/1, side 0), and in the serial interface (RTS, DTR).

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Printer Connector

The Atari uses a standard 25 pins D-SUB Female connectors with the following pinouts (the last column showsa standard PC parallel interface connector for comparison).

Pin ST Connector Standard PC Connector
   
1 STROBE STROBE
2 Data 0 Data 0
3 Data 1 Data 1
4 Data 2 Data 2
5 Data 3 Data 3
6 Data 4 Data 4
7 Data 5 Data 5
8 Data 6 Data 6
9 Data 7 Data 7
10 N/C Acknowledge
11 BUSY BUSY
12 N/C Paper End
13 N/C Select
14 N/C Auto feed
15 N/C Error
16 N/C Initialize
17 N/C Select In
18 GND Signal Ground
19 GND Signal Ground
20 GND Signal Ground
21 GND Signal Ground
22 GND Signal Ground
23 GND Signal Ground
24 GND Signal Ground
25 GND Signal Ground

As you can see the Atari I/F is missing the signals on pins 10 and 12 to 17.

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Printer Cables

It is possible to use a "standard printer cable" with the Atari. Many of the wires are not used due to the fact that several of the standard parallel port pins are not connected as already mentioned. Most printers from this time (like the EPSON LX800) where using a 36 CENTRONICS female connector. Therefore the most commonly used cable was the DB25M to CENTRONICS 36M printer cable.

Special Cables using the Printer Interface

The printer interface provides an easily programmable bidirectional interface to the external world and was therefore used in several projects.

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The PARCP Cable

The printer interface is used by several solutions to provide a fast communication channel between two computers (up to 100KBds).

Several of these solutions are using the PARCP cable:

A description of this cable can be found at the PARCP site. it is basically a DB25M-DB25M data-switch cable (with all pins connected directly on both side) where the wires connected to pins 1 and 11 are switched on one end. This results to data signals connected bit to bit and strobe from one side connected to the busy on the other side plus of course the ground.

Signal Name DB25 DB25 Remark
Strobe / Busy 1 11  
Data 0 2 2 10K resistor can be inserted
Data 1 3 3 10K resistor can be inserted
Data 2 4 4 10K resistor can be inserted
Data 3 5 5 10K resistor can be inserted
Data 4 6 6 10K resistor can be inserted
Data 5 7 7 10K resistor can be inserted
Data 6 8 8 10K resistor can be inserted
Data 7 9 9 10K resistor can be inserted
N/C 10 10 Connected or not
Busy / Strobe 11 1  
N/C 12-17 12-17 Connected or not
Grounds 18-25 18-25 At least one on pin 25

FYI: I have successfully used the PARCP program with this cable, but I did not succeed with HDD_DMN3 program, and I did not try the other solutions (St-Trans and Plip).

Note that the data signals (pins 2 to 9) are connected to bidirectional ports on both side, and they are usually initialized to the default output mode (usually a printer is suppose to be connected to this port) with an unpredictable value (i.e. 0 or 1). Therefore it is possible that any particular data bit from an output on one side is at 0 and on that the output on the corresponding other side is at 1 (or vice-versa) resulting in an electrical conflict. Electronic interface circuits are relatively tolerant but this situation should be time minimized by either setting the ports into the input mode during startup of the computers (programs are provided as part of the PARCP solution for this matter), or by inserting a 1 KOhm to a 10 KOhm resistor between each data signals. For that matter a 8 x 10K resistor pack can be inserted inside a connector on one side.

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The BLITZ Cable

To create backup of "copy protected disk" the BLITZ solution uses a special cable and software to backup protected disk. You must have an external drive to use the BLITZ solution but there is no internal wiring or modification done to the computer. The BLITZ cable copies from drive 1 to drive 2 using at the same time the disk an printer interfaces (it reads Drive 1 and writes Drive 2 at the same time). The BLITZ solution allows to backup protected and non-protected disks.

To use the Blitz program you need an external floppy drive and a special cable. On one end you have a DIN14 female connector that is connected to the external floppy drive. From this connector you will have two cables: one going to a a DIN 14 male connector pluged into the Atari FD connector, and another one going to a D-SUB25 male connector that plug into the Atari parallel connector. Here is a picture of a blitz cable. The layout of the cable is the following:

DIN14M @ Atari FD DIN14F @ Ext. FD DB25M @ Atari Parallel Interface
  1 - Read Data  
  2 - Side 0 Select 2 - Data 0
3 - Logic Ground 3 - Logic Ground  
  4 - Index Pulse 9 - Data 7
  5 - Drive 0 Select 3 - Data 1
  6 - Drive 1 Select 3 - Data 1
  7 - Logic Ground 20 - Ground (18-25)
  8- Motor On 7 - Data 5
  9 Direction In 6 - Data 4
  10 - Step 5 - Data 3
1 - Read Data 11 - Write Data  
  12 - Write Gate 4 - Data 2
  13 - Track 00 11 - Busy
  14 - Write Protect 8 - Data 6
Shield Shield Shield
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ATARI DMA INTERFACE

This interface allow to connect up to 8 external devices with a speed of up to 1MBytes / Sec. The interface is also called the Hard Disc interface because usually it it used to connect hard-disk, or the ASCI interface because it uses an Atari's proprietary hard drive connector/protocol similar to SCSI (which was standardized later) but unfortunately is not directly compatible.

The DMA interface takes its name from the fact that it is connected internally to one of the Atari specially design circuit: the DMA circuit.

The main signals are:

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DMA / Hard disk connector

The DMA/Hard disk interface uses a very unusual and hard to find D-SUB 19 female connector.

 
Pin Name
1 Data 0
2 Data 1
3 Data 2
4 Data 3
5 Data 4
6 Data 5
7 Data 6
8 Data 7
9 Chip Select
10 Interrupt Request
11 Ground
12 Reset
13 Ground
14 Acknowledge
15 Ground
16 A1
17 Ground
18 Read/Write
19 Data Request
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Hard Disk Cable

To connect a hard disk like an Atari SH204/205 or a Megafile drive you will need to DB19M-DB19M Cable.

DB19M @ computer DB19M @ Hard Disk

All matching pins are directly connected from 1-1 to 19-19).

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ATARI FLOPPY DISC INTERFACE

As we will see the FD interface uses a very uncommon a hard to find DIN14 female connector. Most of the signals of this interface are connected to the Floppy disc controller chip (FDC) the Western Digital WD1772. Only few other signals are connected to the Sound circuit as shown in the parallel interface.

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Floppy Disc Connector

Pin Signal Name  FD Connector - DIN 14 Female
1 Read Data
2 Side 0 Select
3 Logic Ground
4 Index Pulse
5 Drive X Select
6 Drive Y Select
7 Logic Ground
8 Motor On
9 Direction In
10 Step
11 Write Data
12 Write Gate
13 Track 00
14 Write Protect

The Atari owners's manual indicates that pin5 is Drive0 Select and pin 6 is Drive1 Select but in fact the signals connected to pin 5 and 6 depends upon the model (STE/STF) and position of internal strap(s) on the motherboard.

By default on both Atari STF and STE the straps on the motherboard are set so that Pin 5 is connected to signal Drive1 Select . This allows to see an external floppy drive, that uses the Pin 5 for selection, as drive B. So the internal drive is A and the external drive is B. This works with most external floppy drive for example a SF314/SF354 from Atari or a CSA354 from Cumana.

On an Atari STF there is one strap W2 that allow to change the signal that goes to pin 5.

On Atari STE it is more flexible because there are one strap W301 that allows to change the signal that goes to pin 5 and another strap W300 that allows to change the signal that goes to pin 6.

It is therefore important to verify that these internal straps are set to meet your requirements.

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Floppy Disc Cable

Usually external FD drive have a data cable coming out directly from the drive without connector and terminated on the other side by a DIN14 male connector that plug into the Atari FD interface.

In some cases it is necessary to use a DIN14M-DIN14M cable. This is the case for example with Discovery Cartridge where the cable is plugged on one side to the Atari FD connector and on the other side to Discovery Cartridge  DIN14F connector labeled Computer. This cartridge is associated with a specific program allow to backup "copy protected disks". In this kind of cable all corresponding pins are connected directly: from pin 1-1 to pin 14-14 as well as the shield of each connector connected to the shield of the cable.

There is also a non standard cable to connect an external FD drive to an Atari called the BLITZ cable (described above).

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ATARI VIDEO INTERFACE

The Atari ST video signals are connected mainly to the Video Shifter circuitry as shown on the right side. The Audio out and GPO signals are connected from the Yamaha YM-2149 sound circuit, and the synchronization signals are coming from the Atari Glue chip.

For an Atari STE the video circuitry has been changed. However it stays close to the ST. Plese refer to the STE Hardware page for more information. For more information about the Atari video and how to connect moder monitor please refer to my Atari ST video page.

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Atari Television Connector

Some Atari models have an RF modulator included (e.g. 520STFM) in this case they are equiped with a special connector for TV. You just need to connect this output to your TV antenna and to tune your TV. This output can also be used with a special box to connect to a VGA monitor.

Core RF Modulated Video
Shield Ground
TV Pinout TV Out Connector
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Atari Video Connector

The Video connector used on the Atari is a rather unusual and very hard to find 13 DIN Female connector. This connector carry out all the video signals (RGB and Sync) as well as audio in and out and a general purpose output pin. The following table shows the pin-out of the Atari 13 DIN Female video connector from the front (external) side. This pictures show DIN13 female connectors and male connector.

PIN

NAME

 

1

Audio out (ST/STE):
This pin is connected to the Atari output amplifier. It normally goes to the Atari monitor sound system; it is possible to connect a 600 Ohms headphone on this output.

2

Composite Sync / Video (STE only):
Not present on early ST. The content of the composite sync/ video output signal is different whether the ST is equipped or not with an RF modulator:

  • If an RF modulator is present (In this case the Atari board contains several extra components - among them is the RF modulator) this signal is a composite video output encoded in PAL or NTSC (Encoding is done in PAL or NTSC based on the country. This is obtained by using different components values and straps on the Atari main board). Note that this signal also contains the combined H & V synchronization signals. This same signal is combined with the audio into the RF modulator.
  • If no RF modulator is present then this signal contains a composite H & V synchronization signals.

3

General Purpose Output (ST):
The GPO pin is connected to the pin 6 of the internal sound chip YM-2149 and can be freely programmed by applications. Usually not used
External Clock Select (STE):
When this pin is grounded the Video shifter takes its clock from an external clock on pin 4.Do not switch clock source while the system is active

4

Monochrome detection (ST/STE):
This pin is connected to pin 17 of the MFP68901 circuit and is used to set the Atari in Hi-resolution when grounded and to Med/Low-resolution when left open. A transition on this pin generates a reset of the system. On a STE pin 3 must be left open for the detection to work.
External Video Clock (STE):
When pin 3 is grounded this input is used to provide an external video clock to the shifter. This allows synchronizing the video-timings with an external device so that a video Genlock device can be used without having to make any modifications to the Atari hardware.

5

Audio in (ST/STE):
An audio signal on this pin is mixed with the Atari internally generated sound and the resulting signal is sent to the Audio output pin 1. Usually not used.

6

Green (ST/STE):
This pin is connected to the green analog output coming from the shifter

7

Red (ST/STE):
This pin is connected to the red analog output coming from the shifter

8

12V / 10mA pin (STE) : On STE this pin is connected to 12V.
GND pin (ST) : On 520STF this pin is connected to GND

9

Horizontal synchronization (ST/STE):
Coming internally from the Glue chip

10

Blue (ST/STE):
This pin is connected to the blue analog output coming from the shifter

11

Monochrome (ST/STE):
This pin is connected to the monochrome output coming from the shifter

12

Vertical synchronization (ST/STE):
Coming internally from the Glue chip

13

Ground

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Atari Video cables

Cables Quality

It is important to use good quality cables to carry the video. The cable must be at least shielded externally, and the color / mono signals should preferably use coaxial wire (especially for long cable like SCART).
Here is an example of a good cable to connect to the Atari DIN13 video output connector. The cable is constructed from three 28 AWG (75 Ohm) coaxial cables plus three 26 AWG twisted pairs and two 26 AWG conductors to ensure signal integrity. Coax cables feature a tinned copper braid providing 93% shield. The cable is shielded by a tinned copper braid providing a minimum of 85% coverage, Mylar® aluminum foil and drain wire to provide 100% coverage.
As pins on the Mini-DIN 13 connector are very packed it is therefore recommended to use heat-shrink tubes for proper isolation of each pin.

The shield(s) of the cable and eventually coaxial cables need to be connected to pin 13 of the DIN connector.

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SCART/Peritel Cable

This cable allows to connect an Atari to a TV equipped with a SCART/Peritel input connector. The cables use on one side a DIN13 Male connector and on the other side it uses a male SCART connector. Both connectors are shown from front side and not from solder side

Signal Name DIN13 male SCART male Remark
   
Audio Out 1 6+2 Audio Left & Right
Composite Sync 2 20 Composite sync
Monochrome Detect 4   Must be left open
Green 6 11 Green in (through 150 Ohms resistor)
Red 7 15 Red in (through 150 Ohms resistor)
12V Pullup 8 8 Audio/RGB Switching
Blue 10 7 Blue in (through 150 Ohms resistor)
V-Sync 12 16 Blanking signal
GND 13 4+5+9+13+17+18+21 Ground

Notes:

  1. If the colors are washed out it is recommended to connect the RGB / Sync signals through 150 Ohms resistors to drop voltage from 1v to 0.7v. On an Atari the RGB output signals already pass through 27 Ohms resistors on an STF and 75 Ohms resistors on an STE, and therefore in most cases these resistors are not required. It is also recommended to connect the Blanking signal through a 75 Ohms resistor. The V-Sync output signals already pass through 33 Ohms resistors and therefore in most cases this resistor is not required. Most of the cables you buy in the commerce do not have any of these pass-through resistors.
  2. Connection of the audio out from Atari to pin 2 is not mandatory as pin 6 is the mono input.
  3. Some people only connect Atari GND (P13) to SCART P21. I believe this is not sufficient and that it is better to also connect pin 4, 5, 9, 13, 17, and 18.
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RCA Composite Video Cable

This cable is useful if you have an Atari ST equiped with an RF modulator. IN that case the Atari produces on pin 2 of its video connector a composite video signal (instead of a composite sync signal). It is therefore possible to use this signal on an equipement that have an RCA composite video signal input (the Yellow or phono input -- see here) like for example the Supera Color HD Box. The White and Red audio RCA plugs are connected to the audio output of the Atari. Here is an example of a RCA Composite video cable.

Signal Name DIN13 male RCA Plugs Remark
     
Audio Out 1 Red & White Audio to Red and White RCA plugs
Composite Sync 2 Yellow Composite video to Yellow RCA plug
Monochrome Detect 4   Must be left open
Ground 13 Shields The shield of all RCA cables should be connected to the Atari Ground

If the colors are washed out it is recommended to connect the RGB / Sync signals through 150 Ohms resistors to drop voltage from 1v to 0.7v.

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VGA Monochrome Cable

This cable allows to connect an Atari operating in High-resolution monochrome mode to a VGA/SVGA Monitor. The cable uses on one side a DIN13 male connector and on the other side a D-SUB15 male connector . The Atari is automatically set to Hi-resolution mode when this cable is connected (pin 4 set to ground). Note that if you want to hear the sound from the Atari you need an extra audio cable (connected to pin 1) going to an audio connector (e.g. a mini jack or RCA connector).

Signal Name DIN13 male DB15 male Remark
   
Audio Out 1   Opt. Audio connector
Monochrome Detect 4+13   Connect to pin 13
H-Sync 9 13  
Monochrome 11 1+2+3  
V-Sync 12 14  
GND 13 6+7+8+10  
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VGA Color Cable

This cable allows to connect an Atari running in Med-Low resolution color mode to a VGA/SVGA monitor. The cables use on one side a DIN13 male connector connected to the Atari and on the other side a D-SUB15 male connector connected to the monitor. The Atari is automatically set to Med/Low-resolution mode (pin 4 left open). Note that if you want to hear the sound from the Atari you need an extra audio cable (connected to pin 1) going to an audio connector (e.g. a mini jack or RCA connector).

Important notice: This solution only works if your monitor accepts a 15.75 kHz Horizontal sync (see Connecting Modern LCD/CRT Monitors to an Atari for the video signals charateristics).

 

Signal Name Atari DB15 Remark
   
Audio Out 1   Audio connector
Monochrome Detect 4   Open
Green 6 2  
Red 7 1  
H-Sync 9 13  
Blue 10 3  
V-Sync 12 14  
GND 13 5+6+7+8+10  
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VGA9 Monochrome Cable

This cable allows to connect an Atari running in High resolution monochrome mode to a VGA multisync monitor with a DB9 connector. The cables use on one side a DIN13 male connector connected to the Atari and on the other side a D-SUB9 male connector connected to the monitor. The Atari is automatically set to Hi-resolution mode. Note that if you want to hear the sound from the Atari you need to have a separate audio cable going to an audio connector (e.g. a mini jack or RCA connector).

Important notice: The cable described here is for a VGA9 Multisync type of Monitor (like NEC Multisync II) but it is NOT for an EGA/CGA (with different pinout) type of monitor (see VGA9/EGA/CGA DB9 Connector)


Signal Name

Atari

DB9

Remark

   

Audio Out

1

 

Opt. Audio Signal

Composite Sync/Video

2

 

 

Monochrome Detect

4+13

 

Connect to Atari pin 13

H-Sync

9

4

 

Monochrome

11

1+2+3

 

V-Sync

12

5

 

GND

13

6+7+8+9

Opt. Audio GND

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VGA9 Color Cable

This cable allows to connect an Atari running in Medium-Low resolution color mode to a VGA multisync monitor with a DB9 connector. The cables use on one side a DIN13 Male connector connected to the Atari and on the other side a DB9 male connector connected to the monitor. The Atari is automatically set to Hi-resolution mode. Note that if you want to hear the sound from the Atari you need to have a separate audio cable going to an audio connector (e.g. a mini jack or RCA connector).

Important notice: The cable described here is for a VGA9 Multisync type of monitor (like NEC Multisync II) but it is NOT for an EGA/CGA (with different pinout) type of monitor (see VGA9/EGA/CGA DB9 Connector). Also this solution only works if your monitor accepts a 15.75 kHz Horizontal sync (see Connecting Modern LCD/CRT Monitors to an Atari for the video signals charateristics)

Signal Name

Atari

DB9

Remark

   

Audio Out

1

 

Opt. Audio Signal

Composite Sync/Video

2

 

 

Monochrome Detect

4

 

Open

Green

6

2

 

Red

7

1

 

H-Sync

9

4

 

Blue

10

3

 

V-Sync

12

5

 

GND

13

6+7+8+9

Opt. Audio GND

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Atari Video Switchers

Atari Monitors Switch box

If you have an Atari SM124 High resolution monochrome monitor as well as an Atari SC1224 color monitor then it is a good idea to use an Atari monitor switcher. This will allow you to switch from one monitor to the other without plugging/unplugging cables. You need a four circuits toggle switch and an enclosure (preferably a metal one) as well as a male DIN13 connector for the cable and two female DIN13 connectors to put on the enclosure. The four circuits of the toggle switch are called A, B, C, D with the input being "in" and the output "1" & "2". For example Ain is connected to A1 if switch is in position 1 and to A2 if switch is in position 2 and of course the four circuits toggle at the same time. This picture show an example of this kind of video switch.

Signal Name Male to Atari Mono connector Color connector
 
Audio Out 1 1 1
Composite Video 2+Bin 2+B1 2+B2
General Purpose Output      
Monochrome Detect 4+Ain    
Audio - in      
Green 6   6
Red 7   7
12 Volts pullup      
Horizontal Sync 9+Cin 9+C1 9+C2
Blue 10   10
Monochrome 11 11  
Vertical Sync 1+Din 12+D1 12+D2
GND 13+A1 13 13

Position1 is the monochrome mode, position 2 is color mode. In summary the connection are:

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Multisync Cable Switch

To use a NEC Multisync II (or Multisync 3D), or for that matter any other multisync monitor that support both the Hi-resolution mode as well as the Med/Low-resolution mode of the Atari ST, you can build a special switch box that will allow you to directly switch between these two (mono/color) modes without the need to change any cable. You need a box (preferably a metal one), a four pole double throw toggle switch, a DIN13 male connector, and a male DB9 connector. A first cable is connected on one side to a DIN13 male connector and on the other side to the box. A second cable is connected on one side to the box and on the other side to a DB9 male connector. The four circuits of the toggle switch are called A, B, C, D with the input being "in" and the output "1" & "2". For example Ain input is connected to A1 output if switch is in position 1 and to A2 output if switch is in position 2. The four circuits of the switch toggle at the same time.

Signal Name connect to atari DB9M to monitor DB15F @ box Remarks
   
Audio Out 1    

audio connector

Monochrome Detect 4+A1      
Green 6+B2 2+Bin 2+Bin  
Red 7+C2 1+Cin 1+Cin  
Horizontal Sync 9 4 13  
Blue 10+D2 3+Din 3+Din  
Monochrome 11+B1+C1+D1      
Vertical Sync 12 5 14  
GND 13+A1 6+7+8+9 6+7+8+10  

Position 1 is for monochrome mode, position 2 is for color mode. In summary the connection are:

Note: If you plan to use this kind of switch box to connect a recent monitor you can replace the cable with the DB9 male connector by a DB15 female connector directly placed on the swich box (last column in blue of the above table). This allows you to connect a recent monitor with a standard DB15-DB15 cable and for a NEC Multisync monitor you will need a special DB15-DB9 cable/adapter. But remember that this solution only works if your monitor accepts a 15.75 kHz Horizontal sync (see Connecting Modern LCD/CRT Monitors to an Atari for the video signals charateristics).

Example Pictures (internals, closed) of the switch I made for my Multisync (note the connector for sound output)

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ATARI MOUSE/JOYSTICK INTERFACE

The Keyboard Interface

Also not accessible from the outside the keyboard is connected to the main board through a connector. The keyboard, mouse, and joysticks are handled by a dedicated processor the 6301 that includes an internal ROM and RAM. The schematic of the keyboard shows how the keys and the mouse/joystick connectors are connected to the microprocessor. The keyboard communicate with the main system through a serial interface a 6850 ACIA.

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The Mouse/Joystick Connectors

The Atari ST has two connectors under the keyboard to connect a mouse or joystick (port 0) and a second joystick (port 1)

The two connectors are DB9M connectors

Mouse/Joystick - Port 0 Joystick - Port 1
1 - Up / XB 1 - Up
2 - Down / XA 2 - Down
3 - Left / YA 3 - Left
4 - Right / YB 4 - Right
5 - NC 5 - Reserved
6 - Fire / Left Button 6 - Fire Button
7 - +5VDC 7 - +5VDC
8 - Ground 8 - Ground
9 - Joy 1 Fire/Right Button 9 - NC
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Mouse/Joystick Switch

Accessing the mouse/joystick connectors is not easy as it is located under the keyboard. However as all programs uses a mouse and most games uses the joystick it is necessary to unplug the mouse and plug the joystick each time you want to play a game and vice-versa. This is obviously not very practical and therefore it is recommended to buy a mouse/joystick switch that allow to connect permanently two joysticks and a mouse and to select with a switch between the mouse and joystick on port 0. This following picture shows this kind of switch.

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Mouse Replacement

TODO : PeST & serial

ATARI STE STEREO AUDIO INTERFACE

The Atari STE has two RCA Audio output ports for stereo (labeled left and right).

ATARI STE JOYSTICK INTERFACE

The Atari STE has two joystick DB15F connectors on the left side of the system.

Port A Port B
01 - Up 0 01 - Up 1
02 - Down 0 02 - Down 1
03 - Left 0 03 - Left 1
04 - Right 0 04 - Right 1
05 - PAD 0 Y 05 - PAD 1 Y
06 - Fire 0 Button 06 - Fire 1 Button
07 - VCC (5V) 07 - VCC (5V)
08 - NC 08 - NC
09 - Ground 09 - Ground
10 - Fire 2 Button 10 - Fire 3 Button
11 - Up 2 11 - Up 3
12 - Down 2 12 - Down 3
13 - Left 2 13 - Left 3
14 - Right 2 14 - Right 3
15 - Pad 0 X 15 - Pad 1 X

Here you will  find an interesting usage of these ports to connect to a PC. From Leonard Site (SainT)

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STANDARD CONNECTORS / ADAPTORS (Non-Atari Specific)

This section presents several connectors/adaptors which are non specific to Atari but useful.

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SCART/Peritel Connector

SCART male SCART female

 

Pin Name Description Signal Level Impedance
1 AOR Audio Out Right 0.5 V rms <1k ohm
2 AIR Audio In Right 0.5 V rms >10k ohm
3 AOL Audio Out Left + Mono 0.5 V rms <1k ohm
4 A GND Audio Ground    
5 B GND RGB Blue Ground    
6 AIL Audio In Left + Mono 0.5 V rms >10k ohm
7 B RGB Blue (S-Video Cup / Pb) 0.7 V 75 ohm
8 SWTCH Status & Aspect Ratio 0-0.4V=off, 5-8V=16:9,
9.5-12V=on 4:3
 
9 G GND RGB Green Ground    
10 CLKOUT Data 2 / Clock    
11 G RGB Green In 0.7 V 75 ohm
12 DATA Data 1/ Reserved    
13 R GND RGB Red Ground    
14 DATAGND Data Ground    
15 R RGB Red (S-Video Cdown / Pr) 0.7 V (Chrom.: 0.3 V burst) 75 ohm
16 BLNK Blanking Signal 1-3 V=RGB, 0-0.4 V=Composite 75 ohm
17 VGND Composite Video Ground    
18 BLNKGND Blanking Signal Ground    
19 VOUT Composite Video Out (S-Video Yout) 1 V 75 ohm
20 VIN Composite Video In / (S-Video Yin) 1 V 75 ohm
21 SHIELD Ground/Shield (Chassis)    

Note: information between parentheses is for non standard extensions.

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VGA DB15 Connector

This is the standard VGA Connector used by most monitors. Information can be found here

DB15 male female @ video card

 

Pin Name Description
1 RED Red Video (75 ohm, 0.7 V p-p)
2 GREEN Green Video (75 ohm, 0.7 V p-p)
3 BLUE Blue Video (75 ohm, 0.7 V p-p)
4 ID2 Monitor ID Bit 2
5 GND Ground
6 RGND Red Ground
7 GGND Green Ground
8 BGND Blue Ground
9 KEY Key (No pin)
10 SGND Sync Ground
11 ID0 Monitor ID Bit 0
12 ID1 or SDA Monitor ID Bit 1
13 HSYNC or CSYNC Horizontal Sync (or Composite Sync)
14 VSYNC Vertical Sync
15 ID3 or SCL Monitor ID Bit 3
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EGA/CGA/VGA9 DB9 Connector

This is the standard used for very old monitors. Note that there are two totally different standards. The VGA9 has been used mainly for Multisync monitors and the EGA/CGA has been used on early IBM machines / monitors.

Male @ monitor cable female @ video card/monitor

 

Pin

Name

EGA Description

CGA Description

VGA9 Description

1

GND

Ground

GND

Red

2

SR

Secondary Red

GND

Green

3

PR

Primary Red

Red

Blue

4

PG

Primary Green

Green

Horizontal Sync / Composite Sync

5

PB

Primary Blue

Blue

Vertical Sync

6

SG/I

Secondary Green / Intensity

Intensity

Red GND

7

SB

Secondary Blue

Reserved

Green GND

8

H

Horizontal Sync

Horizontal Sync

Blue GND

9

V

Vertical Sync

Vertical Sync

Sync GND

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S-Video Connector

This connector (Ushiden connector) is used to carry the S-Video signals.

 

Pin

Signal Name

Remarks

1

GND

Ground Y

2

GND

Ground C

3

Y

Intensity (luminance)

4

C

Color (Chrominance)

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DB15 to DB9 Adaptor/Cable

This can either be an adaptor (usually DB15 male to DB9 Female) or a cable (DB15 male to DB9 male) which is used to connect an old monitor with a DB9 female input to the output from a computer with standard VGA DB15 female connector. See pictures here and here.

Signal Name DB9 DB15
 
Red 1 1
Green 2 2
Blue 3 3
H-Sync 4 13
V-Sync 5 14
GND 6.7.8.9 6.7.8.10
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SCART to S-Video / Composite Adapter

This adapter is used to convert from/to SCART to/from S-Video or Composite. It is usually provided as a box with a 3 circuits switch, one or two SCART connector(s), a S-Video connector, 3 RCA composite connectors (Yellow, Red, White). The 3 circuits of the toggle switch are called A, B, C with the input being "in" and the output "1"& "2". For example Ain input is connected to A1 output if switch is in position 1 and to A2 output if switch is in position 2.


Signal Name

SCART

S-Video (Y/C)

RCA (Y / R / W)

Audio out(right)

1 + C1

 

Red + CIN

Audio in (right)

2 + C2

 

 

Audio out (left)

3 + B1

 

White + BIN

Audio out (right)

6 + B2

 

 

Audio GND

4

 

GND (White + Red)

RGB GND

13

2 (GND C)

 

RGB Red / S-Video C

15

4 (C)

 

GND

17 + (18)

1 (GND Y)

GND (Yellow)

Composite / S-Video Y

 

3 (Y) + AIN

Yellow

(Composite / S-Video) OUT

19 + A1

 

 

(Composite / S-Video) IN

20 + A2

 

 

Position 1 is Output (SCART to S-Video), Position 2 is Input

Audio on RCA (Red and White) are switch from/to SCART Audio in or out Composite on RCA (Yellow) is switched from/to SCART Composite in or out S-Video Color (4) is always connected to SCART Red / S-Video C out S-Video Y Luma (3) is switched from/to SCART S-Video Y in or out.

It is highly not recommended to open this kind of video adaptor. Plastic is sealed and breaks during opening and wires are very fragile. See an opened adapter below.

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CONNECTORS & CABLES LINKS

Some links to sites that provide useful information related to cable and connectors ...

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