PET 2001 E6 Connection Question

[week3]

Ensure that the RCT is not powered by USB (or use a good USB power supply that delivers 5v). USB delivers 5v +/- 10%, and CBM roms are very cranky when the voltage is too low (sometimes you cannot read these reliable when the voltage is below 4.8v).

Ooh good call. The used one I got came with a USB wall wart and i've been using that. Ill test hooked up to one of my variable DC supplies and see if it changes any of the results! Of course im not saying they are bad bad until they fail in circuit once I get to their circuits. But I just marked them with red tape to speed up debugging once I get to those circuits. But yah ill be more cognizant about powering the RCT.

As far as updates go on debugging I'm currently waiting on parts to make the rom adapters. With Chinese New Years. I don't expect to have the PCBs I ordered for a little. Will update yall with the next saga.

 

[week3]

All the parts for the ROM adapters finally arrived!
Jameco accidently sent a 2716 UV EPROM (16kB) in place of one of the five 2732s (32kB) which is one of the most fortunate part swaps they could have done because it still works for this application lol.

After asking BP micro systems for an account I was able to get the BPM 1410 programmer sitting in a dusty corner of my office to program them. Still works despite being last calibrated in 2008 with their latest version of PC software too!
One of my coworkers was even able to find a UV eraser for me.

Messed up a little programming them but fixed it. (Tried programming the original binaries instead of binaries that repeated in order to read out correctly for the adapters).



I replaced the character ROM (A2) with a adapter and the video SRAM(C3) that was suspect while I was in there and it looks like it worked!


The video circuitry is starting to look good so I can start focusing, after all this time, on debugging the actual computer .
I think I should do some work using your method @daver2 and pull the outputs of the video SRAM down to produce a single character to make sure the new character ROM isn't just putting out garbage.
So while im out of time today it will the the first thing I try working on it again. However I did get excited by this progress and try replacing the other ROMS that were suspect with adapters (H2,H3,H4,H5) and various suspect socketed SRAMS.
No dice. Same garbage screen slightly different assortment of garbage characters.

So back to the drawing board gonna study the circuitry and start going through this with a logic analyzer again. But that's the update I have for now. Feels good to be back on this after waiting so long for parts.

 

[daver2]

Actually, that display is pretty good to start with!

You can do the trick with the video RAM output resistors if you like to give you more confidence.

I will post the next steps shortly for you.

Dave

 

[daver2]

I would now concentrate on the pins of the 6502 CPU (F3).

Pin 2 (RDY) should be permanently HIGH.

Pin 4 (/IRQ) should be permanently HIGH or PULSING, not permanently LOW.

Pin 6 (/NMI) should be permanently HIGH.

Pin 38 (SO) should be permanently HIGH.

Pin 37 (Phi0) should have a 1 MHz clock.

Pins 3 and 39 (Phi1 and Phi2) should both have a 1 MHz clock.

Pin 40 (/RES) should be permanently HIGH when at power. If you power the PET up (after it has been OFF for a while) pin 40 should stay LOW for approximately 0.5 to 1.0 seconds after applying the power. This is the power-on reset. You can simulate a power-on reset by using a 100 (ish) Ohm resistor to short out capacitor C6 (0.1 uF ceramic disc capacitor) near the 555 timer UDE9. It is usually good practice to attach a normally-open push-button in series with a 100 Ohm (or so) resistor and to solder this across capacitor C6. This avoids the constant power cycling on the PET if you need to reset it. A 'soft reset' can prevent subsequent damage from the constant power cycling.

Pin 7 (SYNC) should be pulsing.

Everything should be as above - with the possible exception of pin 7. This pin will dictate what we do next.

Just thinking one step ahead. Is the 6502 CPU in an IC socket? Do you have a spare 6502 CPU available and have you come across a NOP generator? Because of the 'sad' state of this PET to start with (and you are winning - much to my surprise), I suspect a logical approach to the initial debugging of the CPU sub-system is probably going to be required. A NOP generator will help us here.

Dave