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Old 16th Apr 2021, 12:06 pm   #1701
ortek_service
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Default Re: Non-working Commodore PET 3016

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The Motorola 1990 book shows it as a direct replacement...
Yes, that's quite helpful - Although technically it shows is that the MC3446AP is a direct or similar replacement for the (Texas Instruments only) MC3446N or MC3446J. However TI themselves claim these area a replacement for the original Motorola MC3446P.

I haven't seen anywhere (yet) where Motorola say the MC3446A(P) replaces the original MC3446(P)
- With no mention of difference in the later datasheets.
But I would expect it to be, and now I've found the original datasheets, I've OCR'd that
(along with TI one, tidying it up so pages are straight & cropped), plus played spot-the-difference on these.

Many of these datasheets are rather vague about operating-voltage range (for Motorola ones) or packages suffix differences (for TI one).


I have now found that the specifications for the original Motorola MC3446(P) & the TI MC3446N (or extremely similar with MC3446J & MC3446D very similar) are basically all the same.

Whereas the later (replacement?) MC3446A(P) has a couple of differences:
- It is compliant with later GPIB / IEEE standard dated 1978 (compared to 1975) and still has termination resistors but only shows 'T' on symbol.
- It has a wider operating voltage range of 4.5-5.5V (compared to 4.75-5.25V)
- It has reduced typical hysteresis on the Receiver Inputs Threshold Voltage High to Low Output Logic State, which is now typically 1.0V rather than 0.8V. (However, it seems they forgot to update the hysteresis-loop graph, as this is the same as before!)

Datasheets for all versions are attached.
Although the TI Datasheet seems to imply that D suffix are also DIL Package, unless TI have changed their package suffix letter meanings, then D was used for (Half-pitch Small-Outline) Surface-Mount.

So although Aliexpress etc have MC3446D's quite cheap, they do show a picture of a Surface-Mount one - So not suitable.

And these are TI's package details that are not in their datasheet, but found from: https://www.ti.com/packaging/docs/se...tipackages.tsp

D (R-PDSO-G16) Plastic Small Outline Package: https://www.ti.com/lit/ml/mpds178g/mpds178g.pdf
J (R-GDIP-T**) Ceramic Dual In-Line Package: https://www.ti.com/lit/ml/mgdi003/mgdi003.pdf
N (R-PDIP-T**) Plastic Dual In-Line Package: https://www.ti.com/lit/ml/mpdi002c/mpdi002c.pdf

So shows that MC3446N or MC3446J would also be OK for original MC3446P
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Old 16th Apr 2021, 12:19 pm   #1702
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Default Re: Non-working Commodore PET 3016

I agree that 'D' almost always means surface-mount, where 'N' almost always means DIP, although confusingly DIP ICs may not always end in 'N'.
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Old 16th Apr 2021, 12:40 pm   #1703
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Default Re: Non-working Commodore PET 3016

I presume we are still agreed that MC3446AP is an acceptable substitute for MC3446N? Otherwise we may be causing Colin some anxiety here in our desire to be meticulous.
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Old 16th Apr 2021, 2:53 pm   #1704
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Default Re: Non-working Commodore PET 3016

I think Colin can rest easy.

Alan
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Old 21st Apr 2021, 2:10 pm   #1705
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Default Re: Non-working Commodore PET 3016

Just to let you all know I have the sockets and new MC3446AP ICs, the keyboard rubberised contact paste and a couple of port connectors for the user port (as I want to add a speaker).

I also have good weather for a change so I'm a bit busy being outside.

I'll be back though soon with an update.

Colin.
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Old 21st Apr 2021, 11:47 pm   #1706
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Acknowledged, Colin. As a regular visitor to Scotland, I know that a spell of good weather there is a gift never to be wasted.

I wonder if you went for a pair of the buffers, or three of a kind?
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Old 22nd Apr 2021, 5:20 am   #1707
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Default Re: Non-working Commodore PET 3016

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On the IEEE subject, is the code on page 184 of this PDF worth typing in to try http://www.1000bit.it/support/manual...EEE488_Bus.pdf Colin.
I used to have that book! I'd forgotten it had a test program. Yes, it would be a great idea to test with that. it will tell you if the IEEE bus drivers are working, and they have been known to fail. It will also check the 6520 that they are connected to.
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On the IEEE subject, is the code on page 184 of this PDF worth typing in to try?
Sorry, I didn't notice that you had tried the super simple test I suggested earlier (The same test is buried in the start of that longer program, which is probably worth typing in and saving since you appear to have a working tape setup). Anyway, the second result should be 255 (same as the number you wrote out in the second instance).

When you write out 255 (decimal) you are sending all 1s (11111111) to the output latches and when you PEEK the port you should see the same bit states coming back, but instead you are seeing 126 which is 01111110, suggesting a possible fault with bits 0 and 7 of the port. Try that program and see what it reports. If it agrees there is a problem we'll drill down and find out whether the problem is with output to the port or readback from the port.

If you POKE 59426,0 and then measure the voltages on the IEEE port 1,2,3,4,A,B,C,D connections all those lines should be 0V / logic 0. If you then POKE 59426,255 and measure the voltages on pins 1,2,3,4,A,B,C,D again, all those lines should now be at logic 1 (~3V or greater).

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OK - typed it in and run it (it makes me miss cut&paste...). As suggested, it reports that the bad GPIB bits are 7 and 0.
Colin.

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I wonder if you went for a pair of the buffers, or three of a kind?
I'd looked at that IEEE book's test program, later on (It'd been OCR'd, looking OK, but I found many wrong chars after pasting elsewhare)
And I discovered it did also check virtually-all the other lines on the port, including the four DAV, NFRD, NDAC and ATN ones that go through the 3rd (UA9) Buffer, and also EOI that has its own extra single output-buffer with direct unbuffered readback. So it's only SRQin that isn't tested - which goes straight to CB1 input on UC6(6520), that also does all of the IEEE Databits as well as some of the other IEEE handshaking lines (with UC5(6522) & UC7(6520) also being used for the remainder).
After reading that User Port article, I had wondered how feasible it would be to fully-test from BASIC all of the lines using the 6520 / 6522's CA1/CA2/CB1 & CB2 - As you can only read the (interrupt etc.) flags set by these, and if the Kernal responds first then it can automatically clear them when it reads the registers. So it seems you can't use the UC5 6522's (User Port) CB2 as an input from BASIC, only as an output, as Port B's Control lines flags may get cleared automatically.

And the older 6520's are actually a right pain to use (compared to more versatile 6522)., with only 2 register select lines - As there's a kind of register bank-switching bit in control registers and also some bits take on different functions depending on setting of Cx2 etc. So I had at first wondered how the single Poke & single Peek that SiriusHardware had listed would work if needing to keep switching the shared Data Direction / I/O Port register address function.
But it's fortunate that Commodore decided to use separate Ports for Data input & output, so the data direction registers for these only had to be setup once in Kernal and you had permanent access to the Data Output & Data Input Port registers without having to keep toggling the register address function.


So if the IEEE book's test program listing only reported Databits errors, then it seems the 3rd (UA9) buffer was still OK, and only UA7 & UA8 ones had failed. But it's not a bad idea to have a spare in case UA9 or one of the replaced Databits ones fails in future as these are getting more difficult to obtain at a sensible price.



When the weather's not too good, then there's quite a few PET games to relive, as featured here: 20 Games That Defined the Commodore PET: https://www.youtube.com/watch?v=YKC8ARAWfhY

Although about the only one I remember playing on one of my School's PET's during after school 'Computer Club' (I don't recall these computers being used for anything else at the time, until we a few years later there was a room of BBC ones) was this version of the Cosmic Guerilla arcade game: https://www.mobygames.com/game/pet/c...ak/screenshots

Last edited by ortek_service; 22nd Apr 2021 at 5:46 am.
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Old 22nd Apr 2021, 5:58 am   #1708
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Default Re: Non-working Commodore PET 3016

I also found the Ruud's Commodore Site has a quite useful webpage about how the IEEE signals work: http://www.baltissen.org/newhtm/ieee.htm

And also some useful info on the 6520: http://www.baltissen.org/newhtm/6520.htm as even full Rockwell (compared to brief Commodore) datasheet on that isn't very clear on the exact operation (Although maybe the MC6821, which has been tested to work the same in these, has a better datasheet)
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Old 22nd Apr 2021, 11:15 am   #1709
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Default Re: Non-working Commodore PET 3016

When I did some part-disassembly of the Kernel and EDIT PROMs I found the CPU jumped into a large subroutine in the EDIT PROM very soon after startup. One of the jobs that first subroutine does is to clear the screen RAM, and another is to set up the 6522 and 6520 ICs in a sane state so that by the time you get to a BASIC prompt those ICs have already been initialised.

I did notice the odd stray signal such as IFC, provided by UA10 pin 10, which has no inherent readback ability to allow it to be self-tested but it is essentially just a buffered reset signal out to the interface so that should not be too hard to check out.

It will come to the point where the only way to be really sure that the IEEE 488 interface is OK is by trying to use it.

That's not to say that we should not fix as many fixable / testable parts of it as we can, first.

Last edited by SiriusHardware; 22nd Apr 2021 at 11:24 am.
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Old 22nd Apr 2021, 1:31 pm   #1710
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Default Re: Non-working Commodore PET 3016

I got three - let's see how it goes with the first two.

I have a few spare chips which I will list soon that other people will be welcome to for their projects.

Colin.

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Acknowledged, Colin. As a regular visitor to Scotland, I know that a spell of good weather there is a gift never to be wasted.

I wonder if you went for a pair of the buffers, or three of a kind?
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Old 22nd Apr 2021, 1:34 pm   #1711
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Default Re: Non-working Commodore PET 3016

I had not twigged they were also known as HP-IB. That takes me back a long way - I used to do IT support for Colman's in Norwich a long time ago. They were a big HP shop with HP 3000s, HP 150 PCs, HP Vectra PCs and servers and all the Thinkjet, Scanjet and other peripherals that all used HP-IBs which were industrial strength and daisy-chainable.

That's when I came across vampire taps for thick ethernet too.

Memories.

Colin.


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I also found the Ruud's Commodore Site has a quite useful webpage about how the IEEE signals work: http://www.baltissen.org/newhtm/ieee.htm

And also some useful info on the 6520: http://www.baltissen.org/newhtm/6520.htm as even full Rockwell (compared to brief Commodore) datasheet on that isn't very clear on the exact operation (Although maybe the MC6821, which has been tested to work the same in these, has a better datasheet)
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Old 22nd Apr 2021, 1:38 pm   #1712
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Default Re: Non-working Commodore PET 3016

I remember Cosmic Jailbreak - thanks for the memory jog. I'll have to go through my tapes and see if I still have it.

A surprisingly high percentage of the games/applications on my 40+ year old tapes still load just fine. I was expecting many more problems with them than I have had.

I guess I ought to somehow make a copy. Is the best way by using my tape recorder plugged into my PC using something like Audacity to create a copy?

Colin.


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Originally Posted by ortek_service View Post
When the weather's not too good, then there's quite a few PET games to relive, as featured here: 20 Games That Defined the Commodore PET: https://www.youtube.com/watch?v=YKC8ARAWfhY

Although about the only one I remember playing on one of my School's PET's during after school 'Computer Club' (I don't recall these computers being used for anything else at the time, until we a few years later there was a room of BBC ones) was this version of the Cosmic Guerilla arcade game: https://www.mobygames.com/game/pet/c...ak/screenshots
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Old 22nd Apr 2021, 1:55 pm   #1713
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Default Re: Non-working Commodore PET 3016

I'm not sure that a conventional tape player will 'play' a PET tape in the sense that you might expect because it isn't really Audio which is on the tape, but a linear series of positive and negative 'bar magnets' which the system lays down on the tape.

I wonder if it is possible to connect two datasettes back to back, data-out on the source connected to data-in on the destination? This is really outside of my experience though.
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Old 22nd Apr 2021, 2:51 pm   #1714
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Default Re: Non-working Commodore PET 3016

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I'm not sure that a conventional tape player will 'play' a PET tape in the sense that you might expect because it isn't really Audio which is on the tape, but a linear series of positive and negative 'bar magnets' which the system lays down on the tape.

I wonder if it is possible to connect two datasettes back to back, data-out on the source connected to data-in on the destination? This is really outside of my experience though.
When I bought a VIC20 (reduced as they were end of line) I couldn't afford a datasette. So I wondered if I could build a bit of an interface to use a normal cassette recorder. I did manage to get something to work but have no idea of the details, except it was probably using CMOS chips, maybe something with a Schmidt trigger input. It was a bit hit and miss, but definitely worked.

I talked about this at an interview at the time, and the interviewer who was also the training officer said they had a spare official one in the cupboard, and gave it to me. So my home made interface didn't get any real use. Oh, and I got the job!
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Old 22nd Apr 2021, 3:04 pm   #1715
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Default Re: Non-working Commodore PET 3016

I'll try the tape-to-computer thing and report back.

Colin.


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Originally Posted by SiriusHardware View Post
I'm not sure that a conventional tape player will 'play' a PET tape in the sense that you might expect because it isn't really Audio which is on the tape, but a linear series of positive and negative 'bar magnets' which the system lays down on the tape.

I wonder if it is possible to connect two datasettes back to back, data-out on the source connected to data-in on the destination? This is really outside of my experience though.
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Old 22nd Apr 2021, 3:24 pm   #1716
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Default Re: Non-working Commodore PET 3016

If you do, you need to use a line-in, not mic-in input on the PC and ideally a line-out rather than 'Ear' or 'Phone' output on the player.

I'm reasonably sure this won't work anyway, but I would be delighted to be wrong, and I don't think any harm can come from trying.
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Old 22nd Apr 2021, 3:52 pm   #1717
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Default Re: Non-working Commodore PET 3016

I've seen programs that will "play" .TAP files from a computers sound card which can be recorded onto tapes and loaded into C64 machines. Since the tape circuit is identical for PET, VIC and C64 machines I think you can record the PET tapes into a computer and play them back. Its a common mod to the commodore tape drives to add a 3.5mm jack to allow audio to be injected into the tape heads to allow playback of TAP files from a phone or computer.

https://www.youtube.com/watch?v=DISA7FrPza4
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Old 22nd Apr 2021, 3:59 pm   #1718
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Another way might be to use a Pi Pico (which has a very large onboard RAM) to read and store the digital data stream played in from a datasette and then send it back out, verbatim, to the same recorder in record mode. There would need to be a bit of level shifting between the datasette's 5V levels and the Pico's 3V levels.
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Old 22nd Apr 2021, 5:00 pm   #1719
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Default Re: Non-working Commodore PET 3016

Many moons ago I successfully recorded C64 and VIC20 tapes using a twin deck audio cassette machine. Worth noting that the datasette doesn't attempt to record digital type signals because it can't. This topic was discussed recently and at some length in the other PET thread.

Alan
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Old 22nd Apr 2021, 7:01 pm   #1720
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Default Re: Non-working Commodore PET 3016

Quick update - I have another datasette (white with a tape counter) which now works after a belt replacement. I have a third datasettes (normal black) which has had the belt replaced and functions electrically (ie it rewinds/ff), but it does not load known working programs.

None of the three datasettes get any power from the PET port 2 - where can I start checking for power please?

Thanks.

Colin.
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