6502 2nd Processor

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KenLowe
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6502 2nd Processor

Post by KenLowe » Sat Nov 30, 2019 12:46 pm

Hi Folks,

Having read this thread, I thought I'd dig out my old 6502 2nd processor, that was gifted to me many many years ago, to see if it looked anything similar to the one being sold, as I recalled it not being a standard. In the end it turns out that it is just a fairly standard 2nd processor, but it does appear to be an earlier rev than the photos online. The odd thing about this unit is that it came in a cheese wedge that claims to be a 16032 2nd processor. Also, I'm not sure if the other 2nd processors typically have the 2nd toggle switch at the rear, which is used to enable / disable the 2nd processor without having to switch it off completely.

Anyway, I thought I'd post up a couple of photos, just in case it's of any interest to anyone...
20191130_122750.jpg
20191130_122803.jpg
20191130_122821.jpg
Edit: Oh, and I WON'T be bidding for the 256k version!

cmorley
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Re: 6502 2nd Processor

Post by cmorley » Sat Nov 30, 2019 12:57 pm

Where does the switch connect? It's a little difficult to work out from the photos - is it between the 5v PSU and the 5v in on the 2proc PCB?

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KenLowe
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Re: 6502 2nd Processor

Post by KenLowe » Sat Nov 30, 2019 1:32 pm

One leg connects to 0v, the other connects to pin 20 of the ULA, which in turn has a 4k7 resistor that connects between pins 20 and 24 of the ULA. Pin 20 of the ULA also connects via a diode to the tube connector (I haven't tried to work out the pin number!). The resistor and diode are clearly an after thought. It looks like pin 20 of the ULA was originally connected directly to one of the pins on the tube connector. This track has been cut, and the diode inserted in line.

I see from the photos on the internet of the issue 4 board, that there is space a 'disable' connector. I guess this is what's been bodged onto my board!
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20191130_130756.jpg
20191130_130819.jpg
20191130_132132.jpg

cmorley
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Re: 6502 2nd Processor

Post by cmorley » Sat Nov 30, 2019 1:44 pm

Ahh that rings a bell.

That's the "disable" jumper according to the schamtic I have here. Pin 31 is a +5v on the Tube so I think the cut track and diode disables the 2proc if the host 5v is not present.

Pin 20 is labelled ~HRST (host reset) on the 80186 and 32016 schematics so the switch and power on the host must force the ULA into reset then...

Edit: HRST also causes PRST says app note 004 so that will hold the processor in rest too.

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BeebMaster
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Re: 6502 2nd Processor

Post by BeebMaster » Sat Nov 30, 2019 3:06 pm

That's very interesting for lots of reasons!

I don't think I've ever seen the shorter, original "BBC Microcomputer" legend on a cheese wedge label before, or even "16O32", with 1O-Downing-Street-style zero. The 16032 soon became known as 32016, although the cheese wedge I've seen refers to neither, calling it the Cambridge Co-Processor (and Acorn badged), so both of these things make it sound like an early case.

Is there a serial number underneath? Presumably any serial number would be related to the 16032 rather than 6502, although I see that inside the box it says "6502 No 18".

The two boards I have pictures of are both issue 4, and this one has an NMOS 6502, they were supposed to be CMOS 65C02s in the second processor, but it could be a replacement chip as it's dated 1981 which predates the 6502 second processor by about 3 years.

The "C" in 6502C part number suggests it might be a 4MHz version:
post-6585-129372498078.jpg
The RAM is socketed (unlike mine) and the IC socket numbers are the same as the 256K version, so although it's a different board, maybe it's just a case of changing the boot ROM and RAM chips to give yourself the extended version!

What is the Tube host code version and is there a dump of the ROM?

I was talking to Hoglet last weekend about Tube host code versions as I was sure I had seen version 1.20. So far I've only been able to find 65C102 Tube host 1.20 in Station 200's internal co-pro, and not in a cheese wedge.
Image

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1024MAK
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Re: 6502 2nd Processor

Post by 1024MAK » Sat Nov 30, 2019 3:32 pm

KenLowe wrote:
Sat Nov 30, 2019 12:46 pm
Also, I'm not sure if the other 2nd processors typically have the 2nd toggle switch at the rear, which is used to enable / disable the 2nd processor without having to switch it off completely.
No disable switch on my 6502 2nd Processor.

Mark

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KenLowe
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Re: 6502 2nd Processor

Post by KenLowe » Sat Nov 30, 2019 3:43 pm

BeebMaster wrote:
Sat Nov 30, 2019 3:06 pm
...or even "16O32", with 1O-Downing-Street-style zero.
I also noticed that!
BeebMaster wrote:
Sat Nov 30, 2019 3:06 pm
Is there a serial number underneath? Presumably any serial number would be related to the 16032 rather than 6502, although I see that inside the box it says "6502 No 18".
Unfortunately, there's absolutely nothing on the back of the case. If you notice, the number 18 is also scratched onto the front of the PCB!
BeebMaster wrote:
Sat Nov 30, 2019 3:06 pm
What is the Tube host code version and is there a dump of the ROM?

I was talking to Hoglet last weekend about Tube host code versions as I was sure I had seen version 1.20. So far I've only been able to find 65C102 Tube host 1.20 in Station 200's internal co-pro, and not in a cheese wedge.
Tube version 0.01??? I've attached a copy. Seems to only use the upper half of the ROM.

I also notice that my board is missing the 74S74 IC27 that is on the Issue 4 board. I feel robbed :lol: :lol: .
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6502Tube.rom
(2 KiB) Downloaded 14 times

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jgharston
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Re: 6502 2nd Processor

Post by jgharston » Sat Nov 30, 2019 8:18 pm

KenLowe wrote:
Sat Nov 30, 2019 3:43 pm
Tube version 0.01??? I've attached a copy. Seems to only use the upper half of the ROM.
It's the standard External Tube v1.10 client code. I've just done a hexdiff with 65Client110 and it's identical.

(The internal CoPro code is functionally identical, just the banner and *HELP message changed, and two of the OSWORD block lengths changed.)

Code: Select all

$ bbcbasic
PDP11 BBC BASIC IV Version 0.25
(C) Copyright J.G.Harston 1989,2005-2015
>_

tom_seddon
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Re: 6502 2nd Processor

Post by tom_seddon » Sat Nov 30, 2019 8:49 pm

KenLowe wrote:
Sat Nov 30, 2019 3:43 pm
I also notice that my board is missing the 74S74 IC27 that is on the Issue 4 board. I feel robbed :lol: :lol: .
I think there's somebody else on here with another one like this one - I'm sure I remember a photo of the circuit board with the missing chip and fuse.

--Tom

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