6502 NOP generator
 

Just found (and ordered) this in case others might need one on future - only £4.80 + P&P.

I wish I knew it existed when I was wrestling with soldering mine.

https://www.laser.com/product_info.p...oducts_id/1981

Colin.

Re: 6502 NOP generator
 

I made a universal NOP generator to test different 40 pin processors, Though I still need to add a clock divider to try it on nmos 6502s and it probably won’t work on Western digital 65C02 as I believe they have cmos input threshold voltages.

Bottom side of the board has 4 of 2x20 pin headers to connect any pin to 5v or 0v, then every pin has a 10k pull up to 5v, and a 1k to a green led down to ground, with pin headers to short any led to ground. Pins will float to between 2.5 and 3v or can be pulled down to 0.5v. Tested so far using cmos and nmos z80s, 8749 and INS8060. A 74hc04 oscillator with a socket to swap in different crystals can be connected to any pin using dupont connector cable but lowest crystal I have is about 1.8 MHz.

Idea was to use this to test a few different micros from my junkbox, but I’ve also used it to check if an 82s131 prom was unprogrammed.

Re: 6502 NOP generator
 

Blimey. That sounds like quite a feat.

Got any photos?

Colin.

Re: 6502 NOP generator
 

Just followed the link Colin and the order total came to £6.00 unit price + £1.20 VAT + £3.00 P&P = £10.20. Not saying that's expensive but for some reason it doesn't tally with the figures you quoted. I'm probably doing something daft.

Alan

Re: 6502 NOP generator
 

The shipping was a fiver. Also the unit price has gone up since I bought mine.

Colin.

Re: 6502 NOP generator
 

Still a good find and should save the obvious frustration caused by the less than reliable home made ones. When you are trying to fix or trace a fault the last thing you need is to have to fix your test gear before you can go on to fix the fault.

Plus, having a completely dependable NOP generator (...and knowing exactly where it is!) virtually guarantees that you will never need it. Think of it as a form of health insurance for your PET.

Re: 6502 NOP generator
 

I think it's one of those small production run things I should buy because it might not be there next time I look.

Colin.

Re: 6502 NOP generator
 

Good point, I have several things like that which I bought because I had no idea how much longer they would be available for.

Re: 6502 NOP generator
 

Don’t forget to test it before you need it, otherwise you won’t know if its the tester or the 6502 at fault.

Re: 6502 NOP generator
 

Attached a few photos of the NOP tester, not sure if the SMT resistors and leds will be clearly visible.

Re: 6502 NOP generator
 

I can only imagine how to do something like that.

Respect.

Colin.

Re: 6502 NOP generator
 

Re: 6502 NOP generator
 

Having bought the Tynemouth board with its older testing software and the lack of NOP testing capability, I'm wondering if I would buy different next time.

It works fine for what I need right now I guess, but I'd do more research next time.

Colin.

Re: 6502 NOP generator
 

Hi Colin,

My collection of 8 bit CPU's, 6502, Z80's and 8085's would end up on a bread board hardwired with the NOP instruction and a 555 timer clock to watch a few led's connected to the address and control lines blink away. I once included a few dip switches on the breadboard to enter a basic program. Of course every time I changed CPU I would have to rewire the breadboard, most frustrating.
What I needed was a contraption that could store a simple program in ram using machine code via toggle switches then release the switches so the CPU can control the address and data bus of the ram. My box features a 2K ram chip, of which only 8 bits are used for a maximum of 256 bytes for program storage, more than enough to get a few leds blinking. I used the tristate feature of the the 74LS244 to connect the toggle switches to the ram. In program mode I enter the address and data, store and move on to the next address. Once the program is entered the 74LS244's are switched to hi Z mode and my breadboard Z80 takes control of the busses. The hex display was added to make it a little easier operate, I mapped the 8 bits to 7 seg displays using an eprom. The DB25 connector on my "Micro assist" is used to interface to the CPU, I also built a simple 4040 counter board to automatically address the ram from 0 to 255 and reset.

My CPU's still end up on a breadboard but at least a little easier to get an led to flash8-\

Hope this is of some use.

Regards

Re: 6502 NOP generator
 

Neat idea am really impressed and love the pics, well done.

Re: 6502 NOP generator
 

Yes that really is an impressive bit of construction and useful as well.

Re: 6502 NOP generator
 

I have a board for a similar function, header is intended to plug into a z80 socket but may need some links changed depending if the target is to generate the clock. Also has an RC2014 interface along the top edge, not populated in the photos attached to the linked thread.

https://groups.google.com/g/rc2014-z...m/tIfVuEaZCAAJ

Single step also works as auto repeat due to the retrigger of the monostable, repeat rate is approx 0.3 seconds, so it can slowly step through code. Another advantage of single step is you can then debug quite a few faults with a multimeter or logic probe.

I’ve considered making a revised version to fix the wire mods as initially I didn’t fully understand the retrigger on reset of the monostable. Changing the monostable to 74ls221 type solved the retrigger but needed a slight mod to the grounding of the RC circuit, instead I changed the circuit to take advantage of the retrigger. I’d probably also increase the size a little to avoid the smt leds as that type doesn’t like hand soldering, maybe also add the single cycle stepper from another of my RC2014 boards.

This board used an old nmos z80, so included buffers to drive address leds and the target board.

I’ve also used this to bootstrap battery backed ram on an RC2014 board to test an INS8073, just to set values in ram for initialising baud rate.

Re: 6502 NOP generator
 

Thanks for info on the laser.com NOP Tester, which I see they are currently out of stock of, but presumably will be getting some more made.
It seems these are frequently required when repairing PET's, as the list it under these even though their 6502-only one would also be usable on Apple / other Commodores that they do parts for.

I see, also under PET parts, they also do 6550 to 2114 RAM-IC converters, to replace the obsolete Commodore-MOS specials, although they'd work out a bit pricey to replace all of them. Not sure what their price is without the 2114 ready-fitted, that they say are also available. But as they just consist of a 74HCT138 on a converter PCB, you could probably get a load made yourself from JLCPCB etc.

They are also selling older EPROM's at quite reasonable prices (£1.30+VAT for 2716's) if these are New Old Stock, now these are obsolete and it seems many obtained form the Far East often do not work.
So if their postage is a flat fee around £5, then there may be a few other items to consider spreading it across.

Re: 6502 NOP generator
 

One thing that always worries me about the 2114 type ram on z80 or 8060 type bus is that they have a R/W control instead of separate OE and WE. Its not a good idea to drive R/W using WE from z80 or WDS from 8060 because both of these processors drive the data bus before the write enable disables the output of the 2114.

Re: 6502 NOP generator
 

All the 2114 pinouts I've seen do call it WE rather than R/W. Although technically it probably is the same, being as they don't have an OE , only a single CS.
However the original MOS 6550 did have a R/W labelled pin and no OE. But (rather-unusually) it did have a Clock (Phase 2?) input, as well as a load of CS / CS pins - Probably just to save Commodore a few address-decoding IC's.
And this was all on a 6502 based system, although Sinclair did use 2114's in the Z80-based ZX81 etc that seemed to work OK.
Although, as 2114's could be as slow as 450ns, then maybe they were a bit tolerant to some glitches on datalines or they were edge rather than level triggered on WE.

I seem to recall when using 6502 R/W to generate Z80 system's RD and WR, then you usually gated with the clock to ensure these were valid. But going the other way, you can only really chose either RD or WR to generate R/W - And maybe need to rely on some CS control.