Are the 2 Vss pins on a 6502 connected internally? Or do they drive separate parts of the chip? I'm designing a circuit on perfboard and I only have space to connect one of them to GND, will that cause a problem? What about then using the other Vss pin to source a Vss on, say, an EEPROM chip? Is it ok to treat them like this i.e. as though there's a regular wire running through the chip connecting them?

  • \$\begingroup\$ Of course you have space to connect both of them! It's a DIP with huge pins and tons of space in between, and you said perfboard not a PCB of limited layers. Perhaps as interesting a question is what you have provided in the way of bypass capacitors. If you want to step outside the norm, remember that for hand assembly you have three dimensions to work with. \$\endgroup\$ – Chris Stratton Jan 8 '17 at 3:27
  • \$\begingroup\$ Actually the perfboard I'm using is Perf+, and I'm specifically trying to demonstrate that it can be used to build a 6502 system without any jumpers, so while I know I could just add a jumper and be done with it, it kinda defeats the whole point of this project. That's why the question is "is it ok to do this" rather than "what are the workarounds I can use to achieve this". \$\endgroup\$ – Mark Feldman Jan 8 '17 at 3:35
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    \$\begingroup\$ Now you just need a kickstarter for an FPGA in a DIP module that emulates a 6502, only with a friendlier pinout. \$\endgroup\$ – Chris Stratton Jan 8 '17 at 3:54
  • \$\begingroup\$ Lol, knowing the way these things work I'd get 2000% funding and blow it all on house renovations. \$\endgroup\$ – Mark Feldman Jan 8 '17 at 4:14

You have to connect them both. Yes, they're connected internally, but that doesn't mean that you can get away with connecting only one of them externally.

And you definitely cannot use them as a pass-through to some other chip.

Why would you have any restrictions on how many pins you can connect on perfboard anyway? It's just more wires, right?

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  • \$\begingroup\$ Thanks for the answer Dave. It's not the answer I wanted to hear, but at least it's an answer. :) To answer your question, I'm designing this system on Perf+ and trying to come up with a design that doesn't require any jumpers or wires at all. \$\endgroup\$ – Mark Feldman Jan 8 '17 at 3:37
  • \$\begingroup\$ Are you trying to put a CPU, a RAM and a ROM all on a single 2.4" x 3.6" board? Good luck with that! What are you using for I/O? \$\endgroup\$ – Dave Tweed Jan 8 '17 at 3:50
  • \$\begingroup\$ Actually I'm using 2 boards stacked, and it's pretty much done apart from this extra Vss pin issue. I/O is a 68B50 chip which I'll talk to with an FTDI cable. \$\endgroup\$ – Mark Feldman Jan 8 '17 at 4:12
  • \$\begingroup\$ Final comment...the project I was asking this for is here: imgur.com/a/nQGwa. Works great now, thanks for the advice. \$\endgroup\$ – Mark Feldman Feb 16 '17 at 7:58

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