software troubleshooter for beeb hardware SelfTestOs

discussion of beeb/electron applications, languages, utils and educational s/w
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marcusjambler
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Re: software troubleshooter for beeb hardware SelfTestOs

Post by marcusjambler » Fri Aug 17, 2018 11:23 am

I spent a bit of time making this test OS run on one of my masters recently.
Its a bit rough... But works fine.
It utilises a standard 27c128 programmed with the standard image posted above.

Once programmed I modified the chip by bending 3 pins clear of the socket and soldering some alternate connections :
master test OS.png

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tricky
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Re: software troubleshooter for beeb hardware SelfTestOs

Post by tricky » Fri Aug 17, 2018 1:24 pm

Those look like mods that would still allow the chip to work in a B or am I missing something?

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1024MAK
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Re: software troubleshooter for beeb hardware SelfTestOs

Post by 1024MAK » Fri Aug 17, 2018 6:24 pm

The Beeb's OS ROM socket uses both /CE (/CS) and /OE, with the different signals coming from separate sources. So no, I don't think it would work without problems.

Mark
Last edited by 1024MAK on Fri Aug 17, 2018 7:58 pm, edited 1 time in total.

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marcusjambler
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Re: software troubleshooter for beeb hardware SelfTestOs

Post by marcusjambler » Fri Aug 17, 2018 7:11 pm

I've just tried it in my Nula beeb and it wasnt happy...

Continuous tone.

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tricky
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Re: software troubleshooter for beeb hardware SelfTestOs

Post by tricky » Fri Aug 17, 2018 10:42 pm

Thanks Mark, I should have realised that those pins might be there for a reason :oops:

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1024MAK
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Re: software troubleshooter for beeb hardware SelfTestOs

Post by 1024MAK » Sat Aug 18, 2018 6:43 am

Hi Tricky

For the BBC A and B machines, the following applies for the OS ROM socket.

/CE ( /CS )
CPU address lines A14 and A15 are decoded by IC21 to map the ROM to the C000 - FFFF range. This is the primary address decoding. This signal tells the ROM chip to get the data from it's memory at the address on it's address line inputs.

/OE
This signal enables the output driver in the ROM for it's data pins. In a Beeb, IC20, IC22, and IC24 perform the address decoding for the I/O device area. IC25 makes it's pin 6 output low only when the CPU is NOT addressing the I/O area. This circuitry is what causes the I/O 'hole' in the ROM area. Note that /OE active with /CE (/CS) inactive has no effect, as the ROM is disabled.

The B+ uses different circuitry, but still has seperate and different signals for /CE (/CS) and /OE.

Mark


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Elminster
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Re: software troubleshooter for beeb hardware SelfTestOs

Post by Elminster » Mon Aug 20, 2018 8:55 am

Interestingly I just ran the Tricky ROM on my Beeb with issues, I shall have put a video over in the relevant thread, not sure I understand what it is telling me. Does all the relay clicking, led flashing and playing tunes as expected. Video result, not surprisingly, are not as they are meant to be.

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