Help for a WE RAM / ROM board not working

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aotta
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Help for a WE RAM / ROM board not working

Post by aotta » Wed Nov 07, 2018 9:18 pm

I bought in the bay a second BBC Micro, reasonable price, with an interesting big black suitcase with Micro siluette for carrying it (yes, a portable beeb diy!) :lol:
I power on it and.... continuos beep! Ok, let's look inside. Open the case and... a varta 3.6 battery rolls away on the table, and a couple of boards start hanging from the motherboard! I realized i got a Micro with Watford 32k ram/rom board and a sideway Watford 32K ramcard! Removed the card, reassembled the original psu cable and roms and... beeb works! Ok... let's try the card. Ok for the ramcard, but... no sign of life with the ram/rom one: when installed, alone or with the ramcard mounted in cascade, i got a "language?" error and nothing else. The manual i found suggests to check the S21 WE link, that is owned by the cards by apposite pins. They are fitted in right way, and have about 4,3v in W and 3,8v in E...
I didn't found schematics of this boards (is there somewhere afyk?) and i don't know how to made further test....
With S21 linked with usual bridge WE, Micro works normally, but cards seems not presets, nor the roms neither the 32k ram.
Any help for further test? Thank you

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tricky
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Re: Help for a WE RAM / ROM board not working

Post by tricky » Wed Nov 07, 2018 9:58 pm

Hello,
I don't know of any schematics, but a picture might help to narrow down which ram/rom board it is (WE made several).

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Re: Help for a WE RAM / ROM board not working

Post by aotta » Wed Nov 07, 2018 10:19 pm

That's the WE ram/rom 128k board:
WERAMROM_front.jpg
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WERAMROM_back.jpg
Last edited by aotta on Wed Nov 07, 2018 10:22 pm, edited 1 time in total.

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Re: Help for a WE RAM / ROM board not working

Post by CMcDougall » Wed Nov 07, 2018 10:26 pm

ahh, the best board! one I still have from BITD, but mine is full of 144k 8)

the two roms in the 2left sockets, they are wrong, they are for the battery backup ram, being 2x 8k in each.
so move the WWise+2 & Mega3 into the other free 2, and also take out the further right one,
as its 32k ram & wont work

hopefully thats it working, will update with a link for the original disc, in a mo when i find it again....
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Re: Help for a WE RAM / ROM board not working

Post by CMcDougall » Wed Nov 07, 2018 10:31 pm

found :
viewtopic.php?f=3&t=8755&p=96318&hilit= ... isc#p96318

your board should be like this, ignore the extra ram top right :
Attachments
watRR144.jpg
2x8k first sockets on left
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Re: Help for a WE RAM / ROM board not working

Post by aotta » Wed Nov 07, 2018 10:38 pm

Thanks for the hints CMcDougall, but it's not the slot the problem.. i made several tests, but even without any roms in the boards i get only the "language?" error...

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Re: Help for a WE RAM / ROM board not working

Post by aotta » Wed Nov 07, 2018 10:45 pm

CMcDougall wrote:
Wed Nov 07, 2018 10:31 pm
found :
viewtopic.php?f=3&t=8755&p=96318&hilit= ... isc#p96318

your board should be like this, ignore the extra ram top right :
Really a monster your WE!
why didn't you fit the battery? you already put the read only switch i se...
if i'll get mine working, i'll add some 4416 drams in the empty sockets!

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Re: Help for a WE RAM / ROM board not working

Post by CMcDougall » Wed Nov 07, 2018 10:53 pm

^ I took the battery out it about 20+ years ago, as knew it would leak & kill my beloved original beeb!

also got another same board that also came with a extra beeb, but did not have the extra ram holes empty,
what a pain in the 'donkey' to clear them out, then put in sockets :x but also now works too with full 144k 8)
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Re: Help for a WE RAM / ROM board not working

Post by DutchAcorn » Thu Nov 08, 2018 5:25 am

Just got the same board in a BBC last weekend. The user guide is here: http://chrisacorns.computinghistory.org ... MBoard.pdf
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Re: Help for a WE RAM / ROM board not working

Post by aotta » Thu Nov 08, 2018 6:22 am

DutchAcorn wrote:
Thu Nov 08, 2018 5:25 am
Just got the same board in a BBC last weekend. The user guide is here: http://chrisacorns.computinghistory.org ... MBoard.pdf
Thank you Paul, but it's the manual I quoted in my first post, and it only relate "language?" Error to S21 link. I had the 2 fixed voltage I reported in east and west (but I only check them with multimeter, I will test with scope now). Can you read the output of them in your working board, to compare with mine?
But s21 is the Rom line control, or it involves the ram line too? I had only "bbc 32k" at boot, so neither the ram is found, so I am confused...

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Re: Help for a WE RAM / ROM board not working

Post by CMcDougall » Thu Nov 08, 2018 8:19 am

^ your beeb will not show 174k, as that's an OS1.20 thing. So 32k on start up is correct & irrelevant of what is in swram banks.
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Re: Help for a WE RAM / ROM board not working

Post by DutchAcorn » Thu Nov 08, 2018 8:32 am

As suggested, please remove the roms that are fitted in the picture. The Winbond is a 64K EEPROM and the two roms in the ROM14L and ROM14H are the wrong type for the socket.

The additional RAM is not reported by the OS but can be paged in and out and is typically used to host ROM images. Look up “sideways ram” for more information.
Paul

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Re: Help for a WE RAM / ROM board not working

Post by aotta » Thu Nov 08, 2018 9:16 am

Thank you, but i am sure it's not a metter of slots or eprom, they work fine in mb slots and in mb other micros, and i tried a lot of combination, included no rom at all on expansion board, getting always the "language? " prompt... 😔

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Re: Help for a WE RAM / ROM board not working

Post by 1024MAK » Thu Nov 08, 2018 9:56 am

The "language? " prompt simply means that the operating system (OS or MOS - machine operating system) cannot find the BASIC ROM or any other “language” ROM. This is typically due to either the BASIC ROM chip not being actually fitted, or a problem with the sideways ROM/RAM control signals going to an expansion board, or the circuitry for these signals on the expansion board. For ROM/EPROM chips fitted to the Beeb motherboard, it could also be a problem with the wiring from the expansion board to the Beeb motherboard that carries decoded ROM select signals to the ROM(s)/EPROM(s) on the Beeb motherboard.

I presume that the BASIC ROM is currently plugged into one of the sockets on the motherboard.

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Re: Help for a WE RAM / ROM board not working

Post by aotta » Thu Nov 08, 2018 10:32 am

Thank you Mark, control signal and control circuit is the direction I intend investigate, since the only case I get basic rom working is when fitted in mb slot and link S21 closed with classic bridge (I.e. not connected to expansion board via dedicated wires). All other combinations port to "language?".

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Re: Help for a WE RAM / ROM board not working

Post by Kazzie » Thu Nov 08, 2018 11:45 am

IIRC, The Beeb looks for a Language ROM (such as Basic or Logo) from the highest priority socket downwards, ignoring non-Language ROMS (such as DFS). If it fails to find one at all, that's when the Language? error comes up, as described by Mark.

Without an expansion board, that search goes from left-to-right along ROM sockets. With an expansion board fitted, the sockets on the expansion board are given higher priority, with the motherboard's sockets given the lowest priority. (This is the case for my ATPL sidewise, and according to the manual linked, your board as well.)

Both these boards replace S21 with a pair of wires to divert the signal that enables IC20 (74ls139), which controls the Chip Select of the motherboard's four ROM sockets.

On the expansion board, the signal is combined with some decoding logic to decide whether to enable one of the expansion ROM sockets, or send the signal back along the other wire to IC20 (for the motherboard's sockets).

If Basic only failed to be recognised in the Motherboard sockets (with expansion fitted) then that might be caused by the "return" wire. But as Basic isn't recognised in any socket, It's likely to be a fault with the decoding logic (or the wire taking the signal to the expansion board).

Check the two wires for continuity. If they're fine, the next step would be to examine the decoding logic. Does anyone happen to have a circuit diagram for this board. Unfortunately, as it's such a complex board it has a lot of 74xx chips, so blind fault-testing or reverse-engineering could take a bit of work.
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Re: Help for a WE RAM / ROM board not working

Post by 1024MAK » Thu Nov 08, 2018 12:01 pm

There are no schematic diagrams available for most of the ROM expansion boards, or for the ROM/RAM expansion boards :twisted:

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Re: Help for a WE RAM / ROM board not working

Post by aotta » Thu Nov 08, 2018 12:08 pm

Thank you Kazzle, you explained very well the rom selection logic, and confirmed most of the ideas I made myself. I have already checked E and W expansion board for continuity, and they are ok from connectors to the two ICs on the Watford card.
So, I am afraid of one or more 74xx failure, but they are all soldered, and it won't be easy find them.
But, do you know how the board compute the rom selection? What voltage or wave I should get in East returning wire?

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Re: Help for a WE RAM / ROM board not working

Post by DutchAcorn » Thu Nov 08, 2018 12:28 pm

Have you tried the board without the RAM chips yet? They are socketed and faulty RAM can cause all kinds of issues.
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Re: Help for a WE RAM / ROM board not working

Post by Kazzie » Thu Nov 08, 2018 1:20 pm

aotta wrote:
Thu Nov 08, 2018 12:08 pm
Thank you Kazzle, you explained very well the rom selection logic, and confirmed most of the ideas I made myself. I have already checked E and W expansion board for continuity, and they are ok from connectors to the two ICs on the Watford card.
So, I am afraid of one or more 74xx failure, but they are all soldered, and it won't be easy find them.
But, do you know how the board compute the rom selection? What voltage or wave I should get in East returning wire?
The signal going through S21 should normally be high (~5V), but drop low (~0V) to enable IC20 (and thus a ROM socket). See this thread for more detail on what voltages would be acceptable.

As for the selection logic, In the plain Model B, IC76 (a 74ls163) reads four bits from the data bus (D0-3) when prompted by a ROM Selection signal from IC26 (another 74ls139). It then stores these four bits, which correspond to to the 2^4=16 possible ROM locations. But because the basic Model B only has four ROM sockets, two of these bits are discarded, and only two are passed on to IC20 for decoding.

Your sidewise board has to reproduce this functionality, but then decode all four bits, for 16 sockets. (A 74ls154 4-to16 decoder would be a likely chip to choose.) As your board plugs in to the CPU socket, it has access to all the pins it needs to replicate the ROM selection signal, as well as the data bus.

On that basis, I'd look for any 74ls139, '154, or '163 chips on your expansion board for a start. (There'll also be some other chips, possibly a 74ls00, involved in choosing whether to send the S21 signal back to the motherboard, but we can leave that for now.)

A good quality photo or scan of your board (with the chip markings legible) would be useful too.
Last edited by Kazzie on Thu Nov 08, 2018 1:21 pm, edited 1 time in total.
BBC Model B 32k issue 7, Sidewise ROM board with 16K RAM
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Re: Help for a WE RAM / ROM board not working

Post by 1024MAK » Thu Nov 08, 2018 1:39 pm

The decoding of the ROM selection latch to provide ROM chip select signals is likely to being done by one or both 74LS138 chips...

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Re: Help for a WE RAM / ROM board not working

Post by Kazzie » Thu Nov 08, 2018 2:01 pm

1024MAK wrote:
Thu Nov 08, 2018 1:39 pm
The decoding of the ROM selection latch to provide ROM chip select signals is likely to being done by one or both 74LS138 chips...

Mark
Good call. (My browser had been loading low-quality versions of the above photos earlier, hence my asking for a photo. How does that Song go? "I can see clearly now...")

A good way to verify that would be to use a multimeter to check for continuity from pin 20 of each of the expansion board's ROM sockets (the chip select pin) to any of the 74ls138s' pins.
BBC Model B 32k issue 7, Sidewise ROM board with 16K RAM
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Re: Help for a WE RAM / ROM board not working

Post by aotta » Thu Nov 08, 2018 2:02 pm

@Paul: a test without ram was one of first things I tried.. No difference
@kazzle & Mark: thanks for all info! I had a little idea of selection logic, made myself while doing the "diy sw ram for under a fiver" in other BBC... Now I have more starting point for testing.

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Re: Help for a WE RAM / ROM board not working

Post by 1024MAK » Thu Nov 08, 2018 2:11 pm

IC1 74LS00 quad 2-input NAND gates
IC2 7414 hex schmitt-trigger inverters
IC3 74LS157 multiplexer
IC4 74LS157 multiplexer
IC5 7400 quad 2-input NAND gates
IC6 74LS393 dual 4-bit binary counter (used for DRAM refresh)
IC7 74LS157 multiplexer
IC8 74LS157 multiplexer
IC9 74LS02 quad 2-input NOR gates
IC10 74LS244 octal buffer, non-inverting outputs (for address bus?)
IC11 74LS244 octal buffer, non-inverting outputs (for address bus?)
IC12 74LS245 octal bus transceiver, non-inverting outputs (for data bus?)
IC13 74LS133 single 13-input NAND gate (address decoding?)
IC14 74LS75 4-bit bistable latch, complementary output
IC15 74LS75 4-bit bistable latch, complementary output (either IC14 or IC15 is likely to be the ROM selection latch)
IC16 74LS157 multiplexer
IC17 74LS138 3 to 8 line decoder (either IC17 or IC18, or both are likely to be the decoders for the ROM chip select lines)
IC18 74LS138 3 to 8 line decoder
IC19 74LS20 dual 4-input NAND gates
IC20 74LS02 NOR gates
IC21 74LS04 hex inverters

Some of the 74LS157 multiplexers will multiplex the CPU address lines for the DRAM chips. Some more 74LS157 multiplexer chips will then switch between the CPU address and the DRAM refresh count from the 74LS393 counter.

Mark
Last edited by 1024MAK on Thu Nov 08, 2018 2:12 pm, edited 1 time in total.

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Re: Help for a WE RAM / ROM board not working

Post by aotta » Thu Nov 08, 2018 2:49 pm

Great work Mark, even better than schematics! I will start this evening from suspect ICs, testing continuity and looking for correct response.. Some works to do!

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Re: Help for a WE RAM / ROM board not working

Post by Kazzie » Thu Nov 08, 2018 3:49 pm

A spot of conjecture of how the "ROMSEL" signal may be generated:

A particular ROM is selected by a program by writing to address &FE30 according to the literature, but the BBC's circuit diagram shows that it only looks at the top 12 bits of the address (so it's effectively mapped to &FE3x).

The expansion board can identify this on the address bus and generate it's own ROMSEL using IC13 (74ls133 13-input NAND) and some of IC21 (74ls04 hex inverter).

One of the 74ls75s (IC14, IC15) can be triggered by ROMSEL to buffer D0-D3 from the data bus. (Based on this post I think the other will buffer A0-A3 to control writing to the RAM banks.)

That then leaves a 74ls157, two 74ls138, a 74ls20 and a 74ls02 (ICs 16-20) to provide the Chip Select decoding (and Output Enable logic) for the expansion board, and/or forward the S21 signal back to the motherboard when appropriate.
Last edited by Kazzie on Thu Nov 08, 2018 3:50 pm, edited 1 time in total.
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Re: Help for a WE RAM / ROM board not working

Post by Kazzie » Thu Nov 08, 2018 4:25 pm

And a spot of further conjecture about those remaining ICs:

S21 should be forwarded back to the board only when S21in is low, as well as the latched values of D2 and D3. So S21out = S21in + D2L + D3L. That's probably done by the 74ls02 NOR gates (IC20).

The other twelve sockets (on the expansion board) can be decoded by the two 74ls138 3-to-8 decoders, with four sockets "overlapping" both decoders:

One with D0, D1 and D2 as select lines, and D3 as an enable, decoding sockets 8-15.

Another with D0, D1, and D3 as select lines, D2 as an enable, decoding sockets 4-7 and 12-15.


Edit: On re-reading the expansion board's manual It considers the expansion RAM as sockets 0-7, the expansion ROM as sockets 12-15, and the Beeb's sockets as 8-11. So the above needs re-evaluating. Perhaps both '138s have D0-D2 as select lines, with one enabled by D3 low (RAM) and the other D3 high (ROM).

------

The Output Enable should go low for addresses &8000-&CFFF (or whenever A15 is high and A14 is low) when the system clock allows. I suspect IC19 (74ls20) is involved.

That leaves IC16 (74ls157) in the middle, but I'm not sure what it would be for.
Last edited by Kazzie on Thu Nov 08, 2018 7:18 pm, edited 1 time in total.
BBC Model B 32k issue 7, Sidewise ROM board with 16K RAM
Archimedes 420/1 upgraded to 4MB RAM (mid- restoration)
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Re: Help for a WE RAM / ROM board not working

Post by aotta » Thu Nov 08, 2018 6:42 pm

Briliant analysis!
i confirm West S21 is connected to IC1 pin 1, and Est S21 to pin 5 IC18 (active low inputs? i expected an output...)
i'll made some test... if only i'll find the probe for my usb scope... it's an hour i am looking for them! :oops:
Last edited by aotta on Thu Nov 08, 2018 6:58 pm, edited 1 time in total.

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Re: Help for a WE RAM / ROM board not working

Post by Kazzie » Thu Nov 08, 2018 6:56 pm

On the BBC circuit diagram, S21 SE is a logic output (low when Sideways RAM/ROM address is on the bus) and S21 SW is the enable input for IC76. So from the expansion board's perspective, S21E is an input and S21W is an output.

Perhaps the output for S21W is generated elsewhere (IC20 perhaps?) but is also used for an input on IC1.
BBC Model B 32k issue 7, Sidewise ROM board with 16K RAM
Archimedes 420/1 upgraded to 4MB RAM (mid- restoration)
Acorn System 1 home-made replica

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Re: Help for a WE RAM / ROM board not working

Post by aotta » Thu Nov 08, 2018 7:09 pm

Anyway, i get this wave at boot for S21 pins from expansion board:
S21WE.png
West go high and stay there...

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