Hi again folks (after some time away!),
When I was a teen, I had an Atari 800 computer/ The Atari did not have a parallel port interface. All they had were the joystick ports, which were serial. A clever company came up with a serial->parallel port interface. Me, not knowing much about electronics, could not figure out how they did this. (PS -I still don't know much about electronics!!!).
Flash forward 40 years and this past week I decided to take apart the serial->parallel interface and reverse engineer this thing! I took apart and there are 2 chips - a 74LS14, and a 74LS164, a resistor and a capacitor. Next step was to draw the schematic, which I did with pencil and paper. This became messy, so I resorted to learning to use KiCad, and came up with the attached drawing. (see attachments)
I get what makes this work is the 74LS164 8 bit parallel-out serial shift register. I still don't really understand how it works though. As I understand it, the data on this register may be read out in parallel (from all flip-flops) at once.
So some questions!
0) Can someone explain how this whole interface works!?
1) How is the data being read on the printer side? Is the printer polling every data pin on the parallel port at once regardless of how many are actually being used?
2) Since there are really only 2 address data pins (3 & 5) being used here, it doesn't seem a vast improvement over serial? But I guess because the Atari only has pins 1-4 for I/O and 1 of those sends the data to the 74LS164?
Thanks for any help understanding this.
Robert Opalko
PS There doesn't seem to be nearly as many members on this forum as there was in the past... Where did everyone go?
