Mods and ROMS

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rune
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Mods and ROMS

Postby rune » Sat Nov 18, 2017 12:49 pm

I've now had a chance to use my Beeb a bit more and make some modifications to it.

The first was to replace the caps in the PSU after a bit of white smoke shortly after turning it on for the first time :)

I've added the following:
A Turbo MMC which is working well,
A variable resistor to adjust the volume
A switch to flick between fairly fuzzy colour and pin sharp monochrome.
A 32K RAM which should give me 2 sideways 16K slots (will test it in a bit as there was no smoke, magic or otherwise).

When soldering the leads from the RAM to the ICs I noticed that pins 11, 12, 13 on IC76? had been soldered as had pin 8 on IC77 at some point. So it looks like someone had done a similar mod before I got the Beeb.

Reading a little further it would seem that Pin 11/12 control addressing and could give 4 sideways RAM or ROM on each socket. Would it be feasible to have a 32K RAM and 2x64K EEPROMS. If so which pins on the chips would pins 11&12 go to?

Would it be better to make a small distribution board so only one wire comes from each pin?

What would be soldered to pin 13?

Finally, is there any way to check what ROM slots are available when no chip or ROM image is loaded?

Dave

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dv8
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Re: Mods and ROMS

Postby dv8 » Sat Nov 18, 2017 4:56 pm

rune wrote:Reading a little further it would seem that Pin 11/12 control addressing and could give 4 sideways RAM or ROM on each socket. Would it be feasible to have a 32K RAM and 2x64K EEPROMS. If so which pins on the chips would pins 11&12 go to?

It's definitely possible but you can only get EPROMs and some Flash ROMs in a 28-pin 64K package. If you want to use RAM or EEPROMs larger than 32K you will need to move up to the 32-pin 128K devices. This will, of course, require an additional 28 to 32-pin socket adapter.

Pin 12 of IC76 goes to A14 on the RAM/EEPROM, pin 11 goes to A15. The pin assignments can be found in the datasheet for your chosen device.

...and wrote:Would it be better to make a small distribution board so only one wire comes from each pin?

It would be better to only have one wire attached to each pin. Rather than a distribution board, you could just wire the address lines between each chip.

...and wrote:What would be soldered to pin 13?

Pin 13 is used to feed IC20 which generates the chip select signals for each ROM. My guess is that it was probably used as a combined chip select for a 128K device. That is, a single 128K chip in the leftmost ROM socket could act like a pair of 64K chips in the leftmost two sockets.

...and wrote:Finally, is there any way to check what ROM slots are available when no chip or ROM image is loaded?

Many utility ROMs include a *ROMS command which will show the ROM banks in use, sometimes they will show the empty banks too.

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myelin
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Re: Mods and ROMS

Postby myelin » Sat Nov 18, 2017 7:20 pm

Here’s the log I wrote about adding 64kB of flash and 32kB of RAM to my Model B... it might come in handy for cross checking purposes even if you’re using different chips: https://github.com/google/myelin-acorn- ... and_ram.md
SW/EE from New Zealand, now in San Francisco: http://myelin.nz/
Having fun making hardware projects for the Electron!
So far: 32k flash cart, USB cart interface, 3-cart expansion, Elk PiTubeDirect. Later: Dual ported ram cart.

rune
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Re: Mods and ROMS

Postby rune » Sat Nov 18, 2017 7:42 pm

Thanks for the help, I've got a 32Kx8 RAM in just now and debugging the ROM load code from the Turbo MMC docs.. Its too dark just now to do anything in the cave re checking pins etc.

I'm now at a stage where the program seems to be doing something, but I don't see any new ROM showing whether on not I select the rest option.

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MartinB
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Re: Mods and ROMS

Postby MartinB » Sat Nov 18, 2017 8:57 pm

(sorry rune, slightly off-topic, but not if you wisely put UPURS in one of your many rom slots :- )

@ myelin - Loving the blog Phillip =D> but just one small point of order if I may....

On your ‘Starting out’ page....

0CC7D5ED-E0D5-4DA3-A295-6512AFBB6F87.jpeg

....on the Beeb and Master, all the UPURS utilities except UPCFS also have disc-based versions so the rom, whilst more convenient, isn’t essential.

Jus’ sayin’... :wink:

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myelin
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Re: Mods and ROMS

Postby myelin » Sun Nov 19, 2017 2:11 am

MartinB wrote:....on the Beeb and Master, all the UPURS utilities except UPCFS also have disc-based versions so the rom, whilst more convenient, isn’t essential.


Hah! I'm prone to forgetting about the existence of discs... I'll add a note to that post!
SW/EE from New Zealand, now in San Francisco: http://myelin.nz/
Having fun making hardware projects for the Electron!
So far: 32k flash cart, USB cart interface, 3-cart expansion, Elk PiTubeDirect. Later: Dual ported ram cart.

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dv8
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Re: Mods and ROMS

Postby dv8 » Sun Nov 19, 2017 10:02 am

rune wrote:Thanks for the help, I've got a 32Kx8 RAM in just now and debugging the ROM load code from the Turbo MMC docs.. Its too dark just now to do anything in the cave re checking pins etc.

A 32K RAM should be straightforward. Pin 27 of the RAM goes to pin 8 of IC77 to enable writing, and pin 1 goes to either pin 11 or 12 of IC76 to provide the second bank.

Sorry if this is stating the obvious but, just to be sure, can you confirm that you are bending up pins 1 and 27 of the RAM chip so they are not making contact with the socket.

The program you are using to write to the RAM will probably ask for a bank number. The leftmost socket (IC52) is bank 12, up to 15 for the rightmost socket (IC101). This is the number for the upper bank of the RAM chip. To get the number of the lower bank subtract 4 (if you wired up to pin 12 of IC76) or 8 (if you wired to pin 11).

...and wrote:I'm now at a stage where the program seems to be doing something, but I don't see any new ROM showing whether on not I select the rest option.

Press the BREAK key after loading the ROM image and enter the command *HELP. The new ROM should be listed. Which ROM are you trying to load?

rune
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Re: Mods and ROMS

Postby rune » Sun Nov 19, 2017 11:49 am

Hi DV8

thanks for getting back. Yes, I bent them up and put heatshrink sleeves on after soldering. I have a 4.7 K resistor from pin 1 to pin 28 and the same from pin 27 to pin 28.

Pin 1 goes to pin 11 on IC77 and pin 27 goes to pin 8 on IC 76.

Im not sure that the image is being loaded correctly, pressing BREAK and *HELP doesnt show anything loaded. The RAM is in the left socket and I try loading to socket 12 and 8.

I'm trying to load language ROMS Abersoft Forth, or Pascal, Multi-Forth and BeebROM are examples.

I found some adapters on ebay that Im getting which will let me use 64K EEPROM and EPROM. Ideally I can use the EPROM as static ROMs and the Flash ROM to load others. The seller has a site containing a program called RTOOL which looks like it would load the ROM, it does show the ROMS and SRAM installed.

I'll check the wiring continuity just in case there is a break. If I can get the RAM working, it will be a bonus.

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dv8
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Re: Mods and ROMS

Postby dv8 » Sun Nov 19, 2017 12:25 pm

rune wrote:Pin 1 goes to pin 11 on IC77 and pin 27 goes to pin 8 on IC 76.

The IC numbers quoted here are the wrong way round. Is this how you have wired it or is it just a typo?

rune wrote:I have a 4.7 K resistor from pin 1 to pin 28 and the same from pin 27 to pin 28.

Try it without the resistors. They are not needed for this mod and may be causing the problem.

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1024MAK
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Re: Mods and ROMS

Postby 1024MAK » Sun Nov 19, 2017 1:00 pm

A resistor is only needed if the control line has a manual enable/disable switch, for example, a write protect switch connected in the line to the signal /WE to pin 27.

But double check, better still, test with a meter to ensure that it is a 4.7k resistor.

Mark
For a "Complete BBC Games Archive" visit www.bbcmicro.co.uk NOW!
BeebWiki‬ - for answers to many questions...

rune
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Re: Mods and ROMS

Postby rune » Sun Nov 19, 2017 1:53 pm

Hi, yes, it is a typo. I think. I followed the wiring in the Doc.

Just fallen out of the loft and hit everything on the way down. I'll check when I stop felling sick and sore.

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1024MAK
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Re: Mods and ROMS

Postby 1024MAK » Sun Nov 19, 2017 6:43 pm

rune wrote:Just fallen out of the loft and hit everything on the way down. I'll check when I stop felling sick and sore.

I hope you are all right [-o<

Mark
For a "Complete BBC Games Archive" visit www.bbcmicro.co.uk NOW!
BeebWiki‬ - for answers to many questions...

rune
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Re: Mods and ROMS

Postby rune » Sun Nov 19, 2017 7:57 pm

Im sore, ladder section wasn't locked in and suddenly I was on a six foot ladder in an 8 foot space. Hit everything that stuck out and the stuff that didn't. I'm fine thanks, but may ache a bit tomorrow.

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myelin
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Re: Mods and ROMS

Postby myelin » Mon Nov 20, 2017 4:27 am

Eep, hope you feel better soon!
SW/EE from New Zealand, now in San Francisco: http://myelin.nz/
Having fun making hardware projects for the Electron!
So far: 32k flash cart, USB cart interface, 3-cart expansion, Elk PiTubeDirect. Later: Dual ported ram cart.


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