Possibly my favourite chip of all time, i use it probably more than anything else in my 80b cpu boards, but having made over 200 new cpu boards now which equals >600 riot chips, i am aware of dwindling real stock and lots of bad/fake/dead ics around being sold as new. The current purchasing of ics has roughly a 1 in 7 reject rate. I currently run tests on each riot before i accept it as good for my boards. This wasn't as bad 5 years ago as it is now and i see it only getting worse over time. As i want to continue to improve and make more 80b cpu boards long in to the future, something new has to be done 
So, this year i am returning to the PIC micro-controller family (used them at various point over the last 20 years, but more recently been on the arduino/teensy wave) to make some emulations of this chip.
The plan is to make a drop in replacement chip using an smd part with an adapter board to fit into the original 40 pin socket. After that phase 2 is to make a single chip that emulates 3 riot ics for use with my 80b cpu boards later. This way i have 2 choices. Projects after this may be to do similar for 6821 or 2 x 6821s, AY-3-8912 and TMS5200 ics, though this is just an idea right now.
Having written some c code and got what i think is a good starting point with something that compiles ok based on the RIOT datasheet i have drawn up a simple adapter board and am waiting for them to arrive before testing begins.
So, this year i am returning to the PIC micro-controller family (used them at various point over the last 20 years, but more recently been on the arduino/teensy wave) to make some emulations of this chip.
The plan is to make a drop in replacement chip using an smd part with an adapter board to fit into the original 40 pin socket. After that phase 2 is to make a single chip that emulates 3 riot ics for use with my 80b cpu boards later. This way i have 2 choices. Projects after this may be to do similar for 6821 or 2 x 6821s, AY-3-8912 and TMS5200 ics, though this is just an idea right now.
Having written some c code and got what i think is a good starting point with something that compiles ok based on the RIOT datasheet i have drawn up a simple adapter board and am waiting for them to arrive before testing begins.
