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This page contains detailed information of how to construct a data cable for transferring data from an Amiga to a PC. This makes possible a whole load of things that are normally very difficult to achieve, including copying individual Amiga files to a PC, and more importantly enables ADF images of Amiga floppy disks to be transferred to a PC. An Amiga emulator data can then used to resurrect those classic Amiga games. This cable was built using a piece of audio cable, couple of old computer serial leads, a pair of scissors, and some tape. Should you wish to follow these instructions, remember that you are doing so at your own risk! Please do not come crying to me if you blow up your computer.
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History
In 1995, my brother and I got an Amiga 500 as a birthday present (We are not twins, but our birthdays are on the same day). As with the ZXSpectrum we had previously, I enjoyed writing software and games for the Amiga. This was a little tricky because time on the computer was shared between us on a time slice basis. After learning how to use the AMOS programming language, I started to write some simple games. The game that my friends remember most is MazeMaster, a 2D Maze game that was quite difficult and had vivid clashing colours that made people feel sick. Except my friend's brother who used a black and white TV as an Amiga monitor. The PC unfortunately forced the Amiga into retirement and was eventually thrown away. However some floppy disks were retained since they contained work and memories of the good old days. A small box of floppy disks remained in storage for several years until at Uni I found other ex-Amiga owners and who were in the same situation as me regarding retrieving their data.
Reading Amiga Floppy Disks
As most Amiga users are aware, the floppy disk format used by an Amiga is incompatible with a PC. This is to do with limitations with the PC floppy disk controller on the motherboard. The Amiga floppy disk controller is very flexible, and although is limited by the data density of the floppy disk drive, can actually read and write to 720k DOS formatted floppy disks with utilities such as CrossDOS. The only proper way to read Amiga floppy disks in a PC is to use a special floppy disk controller, and these tend to be expensive and hard to come by. Amiga floppy disks can be stored into a special file format called ADF (Amiga Disk Format). The ADF file format is the most compatible in terms of PC Amiga emulators, and is the standard file format used by Amiga game download websites. Unfortunately it is not possible to store an ADF file on a 720k DOS formatted floppy disk due to the ADF file being too big, even after compression. Splitting the file into two halves is another option, however utilities to do this can be difficult to find.
Data Cable
Using a data cable overcomes these limitations, and speeds up the process of transferring ADF files to a PC. There are various commercial products available for this purpose, but care must be taken in order to choose a compatible product, see the Smoke Warning section below. A simple home brew cable can be constructed by splicing together some scrap serial cables. The wiring for a data cable is relatively simple, requiring just two connections to be made, DATA and GND.
Smoke Warning
Amigas uses a non-standard serial port configuration. Some pins that are conventionally ground (0V) are used on the Amiga as supply voltage outputs for peripherals. For example, pins 9 and 10 on the serial port are connected to the power supply, and have 24 Volts between them. Most standard serial leads make connections to these pins assuming that they are ground. If a standard serial cable is used, this will short circuit the Amiga power supply, often at the PC end of the cable where they are all grounded inside a PC serial port. If this happens, the Amiga/PC produces a burning smell, and the power supply makes a hissing noise.
Do Not Under Any Circumstances Use Standard Cables With An Amiga!
Fortunately, when I did this luck must have been on my side because I realised what was happening in time, the fire brigade did not have to be called, and the Amiga and PC both survived to tell the tale.
Step-by-Step Guide
This is the step by step process followed while constructing the cable...
Obtain correct pin-out connections for the RS232 Ports
The diagram in the Data Cable section should be sufficient for a conventional Amiga->PC connection. If the serial ports used are different from those depicted, an internet search may be required.
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Prepare the Cables
This was achieved using two discarded computer cable ends that had the correct connectors for the ports, and a length of audio cable long enough to reach between the two computers. The audio cable plugs were not required and were cut off - don't throw them away as they may be needed for a future project!.
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Open the Back-shell
Reveal the wire colour to pin mapping by opening the back-shell. If the cable has an injection moulded back-shell that cannot be opened, a continuity tester must be used in order to locate the correct wires.
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Remove the sheath
Carefully cut through the outer layer of plastic a few centimetres from the end of the cable. Remove the sheath to expose the screening braid wire by sliding it off the end. Take care not to cut your fingers, or damage the wire strands.
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Separate the Relevant Wires
The relevant wires are connected to pins 2 and 5 on the 9 way connector, and pins 2 and 7 on the 25 way connector.
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Strip the Wires
Strip some insulation from the wire, again taking care not to cut your fingers or excessively cut the strands of wire.
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Join the Wires
Connect the GND to the screening of the audio cable, this is pin 5 on the 9 way connector and pin 7 on the 25 way connector. Attach the DATA wire to the inner core of the audio cable, this is pin 2 on the 9 way connector and pin 2 on the 25 way connector. Refer to the wiring diagram in the Data Cable section. A sufficient connection can be made by simply twisting the strands of wire together.
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Apply Insulating Tape
It is important to insulate all exposed wire using tape. This is to prevent the wires from shorting to each other and to other metallic items such as exposed metal areas on the computer chassis. Use the tape to make a secure mechanical strain relief to prevent the wires from pulling apart, then close the back-shells of the connectors.
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Configuration
No special software is required at either end in order to copy files between computers. To test the link, boot the Amiga up into Workbench. In the Serial preferences, set the Baud Rate to 19200, turn parity off, and set the communication to 8 bits and 1 stop bit. On the PC, do the same by issuing the following command in a shell:
stty -F /dev/ttyS0 19200 raw
The serial link should now be configured, and data can be sent from Amiga to PC.
Sending
On the Amiga, the ser: device is used to access the serial port. To copy a file to the serial port, issue a command similar to this in a shell:
copy filename.txt ser:
The shell prompt will return after the file has copied. Redirections can also be used to send data to the serial port for example:
dir > ser:
This will send the output of the dir command (a directory listing) to the serial port.
Receiving
To receive the data on the PC, use the cat command. The PC must be waiting to receive the data before the Amiga starts to send, otherwise some data will be lost. To receive data, and print it to the console issue the following command in a shell on the PC:
cat /dev/ttyS0
Issuing the dir command in the example above will result in the directory listing of the Amiga appearing on the PC console. Unfortunately, at the time there wasn't a suitable monitor to display the output of the Amiga, so a TV built some time ago was used. This used a 9mm screen from a camcorder viewfinder, which made it difficult to take good quality photographs of the display.
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After the data has been received, the cat command at the PC end will continue waiting for new data. This is because the port is in RAW mode which is required for the transfer of binary data. Once the data has been transmitted, press ctrl-c on the PC to stop cat. To save data into a file on the PC, issue the following command:
cat /dev/ttyS0 > filenname
This is best used in conjunction with the copy command used above. Remember to press ctrl-c when the file is finished.
ADF Files
These are used by emulators such as UAE, and contain an image of an Amiga floppy disk. With this configuration, ADFs have to be created by the Amiga. An Amiga program called ADFBlitzer can be used to create ADF files. This can be copied to the Amiga on a 720k dos formatted floppy disk in conjunction with the Cross-DOS Amiga utility.
ADFBlitzer is a shareware/freeware utility that can be downloaded from many of the free download sites, use your favourite search engine to locate a copy. After running the ADFBlitzer program on an Amiga and the 'Read' option is selected, a screen prompts for a location of where to store the ADF file. The file name should be specified in ADFBlitzer as ser: which causes ADFBlitzer to write the ADF file over the serial connection to a file on the PC. Higher baud rates were tested with this simple cable and the communication link still appeared to be error free. It should be noted that communication errors will not be detected using this method of communication. For this reason it is probably worth sending two copies to the PC and compare them using diff. If there are no differences, it can reasonably safely assumed that no data corruption has occurred.
Contact
If you have any comments or suggestions, please contact me craig@microtron.org.uk
