48-bit ISA parallel I/O card

I constructed this card on a ISA prototyping card. This was to be one-time project so I did't design the PCB lay-out artwork. I/O lines come out with 50cm Twisted pair flat cable (every other wire is GND). The card is tested with 486DX-2 80MHz PC with 8MHz ISA-bus clock.

I contructed also a 8-bit optoisolated I/O module to be used with this card. The card is constructed to 10 x 16 cm prototyping board. The optoisolators are very likely to be obsolete. I found them in my junkbox. Only drawback is that all bits in output are reversed. When the input voltage is over the reference voltage the output bit is low. A inverter on all bits would cure this.

Note that all bigger files have .gz ending meaning the fact that they are compressed with gzip (Gnu compresser).

The .SCH file is in OrCAD SDT 4.10 format. Used libraries are standard: INTEL.LIB, TTL.LIB, DEVICE.LIB, and ANALOG.LIB

Design files

C-source code to use and test the I/O card

Here is some test programs (C && MS-DOS) I have used to test and use the card.

Netlist formats

Here are some netlist formats created from the ISA8255.SCH by OrCAD. As I have not used these myself I can not guarantee they are working. Use them at your own risk.

Some notes about the design:

The resistors are separate and not a resistor pack as it might look like at the schematic.

The connectors 0A, 0B, 1A, and 1B are not real connectors, but wires with a junction at the end. I have not checked but they may be missing from the netlist (these wires are all dataports A, B, and C from both PPI's).

I connected +5V from the ISA-bus thru a 50 ohm resistor to the unconnected pin at the connector. This pin used to power the opto isolator inputs. The resistor limits the possible short-cicruit current so the power supply will survive (but the resistor will not).

I used 74ALS244 buffers as I had them (got three tubes practicly for free) at my junkbox. I calculated the timings using these but I guess the LS244 will do as well.

Datasheets for 82C55A by Harris and Intel

Harris has PDF and PostScript format datasheets for 82C55A at URL: http://www.semi.harris.com/data/fn/fn2/fn2969/index.htm. I have not compared this new CMOS version with the older I used but I guess that they are pretty similar...

Intel has also PDF datasheets for 82C55A at URL: http://developer.intel.com/design/periphrl/datashts/.

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Page updated 1998-01-23