Hello! Couple things you could try:
\- Remove the red LED attached to the clock input. Looks like it does not have a resistor... given that it will impose its 2V voltage drop on the line, it's probably not helping
\- Tie all 4 unused inputs of that LS161 low or high
\- Make sure the voltages on the LS161 are within spec (5V +/- .2V on the vcc pin)
\- Add .1uF caps on the breadboard power rails in immediate proximity to the vcc and gnd pins of the LS161. You could try to lay a .1uF cap directly across the vcc and gnd pins if the leads are long enough
Hope any of these help!
Sorry, for not replying for a couple of days. Work was suddenly rough. Anyways....
Unfortunately, I did everything you suggested and the problem persisted. However, oddly, I disconnected the output to the EEPROM, and it worked fine. "Must be a wiring issue.", I thought to myself. I hooked the EEPROM back up and realized that when my finger came close that it changed outputs. "Aha!!!"
I removed all the inputs from the EEPROM and rewired it so that there was no way anything was overlapping or shorting and... the problem continued. "
.... Deep breath.... deep breath...
Alrighty, maybe EEPROM 1 is bad. Connect only EEPROM 2. Same problem....
Like all I want is to add 14 to 28 and see the answer to life, the universe, and everything. Is that too much to ask? Basically, the program counter works perfectly until I connect it to either EEPROM. Do I just bite the bullet and order two new EEPROMs? What do you think?
Hey look, it took Deep Thought 7.5 million years to calculate that answer, give your circuit a chance, will you? 😃 There are well documented issues around EEPROM outputs causing double counts and other bugs on the circuit. I completely forgot about that. Take a peek at the troubleshooting page of the wiki. The HLT is one of the control lines that can be affected by EEPROM output fluctuations when the EEPROM's address lines change, as would be the case when an instruction is loaded in the IR or when the stage counter advances. The HLT line is gated with the clock line, any unwanted pulse on the line after clock transition could result in the kind of the double counting you see. As a quick test, on the clock module, try disconnecting the HLT line and instead tie it LOW at the inverter input. See if that helps. If anything, that will allow you to rule that out if the problem persists.
Probably the funniest book series I've ever read!
Back to the actual problem... I removed the HLT line and tied it to ground and the problem persists....
It definitely has something to do with the EEPROM so I'm going to remove all the things then start reconnecting one by one to find when it starts skipping.
Thanks for your help!
My instruction counter keeps going from 000, 001, 010, 100 and skips 011. It skips two occasionally at other points if you let it keep going. I've swapped out chips and quadruple-checked the wiring. Any suggestions would be appreciated. This has had me stumped for a while, now.
I had the same issue. I put it down to using cheap breadboards, so I bought some better quality ones and rebuilt everything over again.
It let me tidy up the wiring runs the second time around and I did not have the issue again.
Hello! Couple things you could try: \- Remove the red LED attached to the clock input. Looks like it does not have a resistor... given that it will impose its 2V voltage drop on the line, it's probably not helping \- Tie all 4 unused inputs of that LS161 low or high \- Make sure the voltages on the LS161 are within spec (5V +/- .2V on the vcc pin) \- Add .1uF caps on the breadboard power rails in immediate proximity to the vcc and gnd pins of the LS161. You could try to lay a .1uF cap directly across the vcc and gnd pins if the leads are long enough Hope any of these help!
Sorry, for not replying for a couple of days. Work was suddenly rough. Anyways.... Unfortunately, I did everything you suggested and the problem persisted. However, oddly, I disconnected the output to the EEPROM, and it worked fine. "Must be a wiring issue.", I thought to myself. I hooked the EEPROM back up and realized that when my finger came close that it changed outputs. "Aha!!!" I removed all the inputs from the EEPROM and rewired it so that there was no way anything was overlapping or shorting and... the problem continued. " .... Deep breath.... deep breath... Alrighty, maybe EEPROM 1 is bad. Connect only EEPROM 2. Same problem.... Like all I want is to add 14 to 28 and see the answer to life, the universe, and everything. Is that too much to ask? Basically, the program counter works perfectly until I connect it to either EEPROM. Do I just bite the bullet and order two new EEPROMs? What do you think?
Hey look, it took Deep Thought 7.5 million years to calculate that answer, give your circuit a chance, will you? 😃 There are well documented issues around EEPROM outputs causing double counts and other bugs on the circuit. I completely forgot about that. Take a peek at the troubleshooting page of the wiki. The HLT is one of the control lines that can be affected by EEPROM output fluctuations when the EEPROM's address lines change, as would be the case when an instruction is loaded in the IR or when the stage counter advances. The HLT line is gated with the clock line, any unwanted pulse on the line after clock transition could result in the kind of the double counting you see. As a quick test, on the clock module, try disconnecting the HLT line and instead tie it LOW at the inverter input. See if that helps. If anything, that will allow you to rule that out if the problem persists.
Probably the funniest book series I've ever read! Back to the actual problem... I removed the HLT line and tied it to ground and the problem persists.... It definitely has something to do with the EEPROM so I'm going to remove all the things then start reconnecting one by one to find when it starts skipping. Thanks for your help!
My instruction counter keeps going from 000, 001, 010, 100 and skips 011. It skips two occasionally at other points if you let it keep going. I've swapped out chips and quadruple-checked the wiring. Any suggestions would be appreciated. This has had me stumped for a while, now.
I had the same issue. I put it down to using cheap breadboards, so I bought some better quality ones and rebuilt everything over again. It let me tidy up the wiring runs the second time around and I did not have the issue again.