BBC Master 128 - Watford Electronics Diagnostic Disk

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Gelpack
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BBC Master 128 - Watford Electronics Diagnostic Disk

Post by Gelpack »

HI

OK, I took delivery of one of these diagnostics disks off eBay against my better judgment, but there you are I did it anyway.

So having had a quick spin, the following questions have arisen.

1.) It tells you to refer to the manual on the RAM test (Anyone know where to find this, I've looked by no banana

2.) The memory test runs OK until it hits &8000 and fails, so I'm not sure what it was ever supposed to do and if this is expected on a master even though it supposed be a 128 ( I'm assuming it should have 128K as the baseline is supposed to be 128k, and actually this brings me onto another question, how do you query the memory available on the master, I've never tried so far . I suspect this might be to do with the fact it does not know how to access sideways rom but im not sure.


Cheers for any help in advance.
Coeus
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Re: BBC Master 128 - Watford Electronics Diagnostic Disk

Post by Coeus »

Unless you have installed a third part extension, the Master always has exactly 128K on the main/IO processor. The Master 128K is described as such to distinguish it from the Master 512 which has a bundled co-processor and the extra memory is on the co-processor.

So the I/O processor always has:
  • The 32K in the lower half of the address space just like the BBC B
  • 20K of shadow RAM for the screen.
  • 12K of extra workspace RAM used by VDU drivers and filing systems.
  • 4 banks of sideways RAM, each 16K
It was only the B+ that could, in the form of the B+ 64K, have the shadow RAM, and a slighly different arrangement of extra workspace, without having the sideways RAM.

Having said that, there are some jumpers that enable the sideways RAM on the Master to be replaced in the address map (not physically) by ROM. LK18 controls slots 4 and 5. When WEST these are RAM, when EAST those slots use the ROM in IC41. LK19 does the same for slots 6 and 7: WEST is RAM and EAST is ROM IC37.
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Gelpack
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Re: BBC Master 128 - Watford Electronics Diagnostic Disk

Post by Gelpack »

Coeus wrote:
Wed Jun 22, 2022 5:59 pm
Unless you have installed a third part extension, the Master always has exactly 128K on the main/IO processor. The Master 128K is described as such to distinguish it from the Master 512 which has a bundled co-processor and the extra memory is on the co-processor.

Thank you for your answers, that is most informative and useful in terms of the memory allocation.
paulb
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Re: BBC Master 128 - Watford Electronics Diagnostic Disk

Post by paulb »

Coeus wrote:
Wed Jun 22, 2022 5:59 pm
Unless you have installed a third part extension, the Master always has exactly 128K on the main/IO processor. The Master 128K is described as such to distinguish it from the Master 512 which has a bundled co-processor and the extra memory is on the co-processor.
The articles "Inside the Master box" and "Private RAM and 50 bytes makes all the difference" (Acorn User, February 1986) are informative here. Also, to remove any ambiguity for anyone reading this and wondering, the Master 512 offers 512K of RAM in addition to all the usual RAM provided by the Master 128, just in case anyone might think that the 512 upgrade merely added another 384K to make the total amount up to 512K.

I only raise this latter point because it seems that for Acorn's ARM-based machines, there were some RAM upgrades that bypassed installed RAM but others that augmented it, this apparently being a distinction between 2MB and 4MB upgrades for the A300 series (see "Memory Lapse", Acorn User, April 1992), whereas A3000 RAM upgrades always seem to have augmented the on-board RAM (see "Augmenting the Arc", Acorn User, September 1990). People familiar with such upgrading approaches might have similar expectations in other situations.

To those of us familiar with the architecture of these systems, it might be obvious why augmenting the 128K of the Master 128 wouldn't have been a sensible approach in trying to provide a 512K-based PC environment, but not everyone opening the lid of one of these things is going to be as familiar with it as we are.
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Gelpack
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Re: BBC Master 128 - Watford Electronics Diagnostic Disk

Post by Gelpack »

paulb wrote:
Thu Jun 23, 2022 12:47 pm
Coeus wrote:
Wed Jun 22, 2022 5:59 pm
Unless you have installed a third part extension, the Master always has exactly 128K on the main/IO processor. The Master 128K is described as such to distinguish it from the Master 512 which has a bundled co-processor and the extra memory is on the co-processor.
The articles "Inside the Master box" and "Private RAM and 50 bytes makes all the difference" (Acorn User, February 1986) are informative here. Also, to remove any ambiguity for anyone reading this and wondering, the Master 512 offers 512K of RAM in addition to all the usual RAM provided by the Master 128, just in case anyone might think that the 512 upgrade merely added another 384K to make the total amount up to 512K.

I only raise this latter point because it seems that for Acorn's ARM-based machines, there were some RAM upgrades that bypassed installed RAM but others that augmented it, this apparently being a distinction between 2MB and 4MB upgrades for the A300 series (see "Memory Lapse", Acorn User, April 1992), whereas A3000 RAM upgrades always seem to have augmented the on-board RAM (see "Augmenting the Arc", Acorn User, September 1990). People familiar with such upgrading approaches might have similar expectations in other situations.

To those of us familiar with the architecture of these systems, it might be obvious why augmenting the 128K of the Master 128 wouldn't have been a sensible approach in trying to provide a 512K-based PC environment, but not everyone opening the lid of one of these things is going to be as familiar with it as we are.
A very illuminating link, complete with Sepia coloured paper background. -

Thank you - Terry
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