The AST Six Pak Plus adds an awful lot to your PC, serial, parallel, RTC, up to 384KB of RAM and optionally a game port. It comes in more than one variation. There is a manual here which covers the original variation of the hardware : http://www.minuszerodegrees.net/manuals.htm
This is my board :
20160510_152708.jpg
Mine is a Type 2 or Type 3 variation, and does not seem to be particularly different from the Type 1 described in the manual. More importantly, there is a complete schematic in the manual for the Type 1.
Previously, I had considered using the method here to obtain bidirectionality : http://www.brutman.com/PCjr/parallel_port.html
However, I ran into two problems with this mod when I first considered it several years ago, but no one here was able to help me. First, my card has two 74LS174s on board. Second, pin 15 on each is connected. Then I discovered the schematic and was able to identify that the '174 at U71 was the '174 assigned to the parallel port interface. I also learned that Pin 7 of that chip is not connected in the Six Pak Plus. It does not appear connected on my board, so now I have my gate. I was a little confused at first given that IBM used pin 7 and not pin 15, but the only thing that matters is that D5 is connected to an input on the '174 and the output is not used. There is only one 74LS373 on the board at U76, which is remarkably convenient.
I have yet to try this mod, but I am confident that it will be successful. If someone else wants to try it or already has succeeded, I would like to hear about it.
This is my board :
20160510_152708.jpg
Mine is a Type 2 or Type 3 variation, and does not seem to be particularly different from the Type 1 described in the manual. More importantly, there is a complete schematic in the manual for the Type 1.
Previously, I had considered using the method here to obtain bidirectionality : http://www.brutman.com/PCjr/parallel_port.html
However, I ran into two problems with this mod when I first considered it several years ago, but no one here was able to help me. First, my card has two 74LS174s on board. Second, pin 15 on each is connected. Then I discovered the schematic and was able to identify that the '174 at U71 was the '174 assigned to the parallel port interface. I also learned that Pin 7 of that chip is not connected in the Six Pak Plus. It does not appear connected on my board, so now I have my gate. I was a little confused at first given that IBM used pin 7 and not pin 15, but the only thing that matters is that D5 is connected to an input on the '174 and the output is not used. There is only one 74LS373 on the board at U76, which is remarkably convenient.
I have yet to try this mod, but I am confident that it will be successful. If someone else wants to try it or already has succeeded, I would like to hear about it.