Sideways Ram

[Becky]

Now that my BBC Micro is up and running I have been playing with the Turbo MMC and even RTFMing it. The documentation is quite detailed and really technical in places. I read a part about how to load ROM images into memory. I tried it and of course it did not work. I have no extra RAM, sideways or otherwise.

I like the idea of loading different ROMS to play with from the MMC, so I wanted to confirm with a view to buying one in a week or two, Is the 32K ROM / 32K RAM module from BooBit the thing I need? I could modify the board to do a Sideways RAM upgrade, but I don't want to touch the board, which appears to be unmodified unless I have to.

[cmorley]

For tinkering with ROM images or playing B games which need SWRAM then yes it is a good solution... if you later want to have ROMs stay across power cycles then a non-volatile solution like an EEPROM is what you need (I do one of those too).

My opinion might be biased as I make the BooBip stuff. There are plenty of solutions out there with varying levels of cost, complexity, simplicity to install/use and levels of support.

[1024MAK]

If you don’t want to modify the board then there are two ways of going about this:

• DIY route
• Plug in module route

The DIY route involves bending some pins up of a suitable static RAM (SRAM) chip so they don’t go into the socket. Then soldering some wires on to these pins. These wires are then connected to other chips on the board. Either via solder connections or by using clips designed to connect to chip pins.

The plug-in module route again has a couple of options. The BooBip module is one. The others are larger expansion boards that fit in one or more of the ROM sockets and with some designs, also in the 6502 socket. They offer more sideways RAM and extra sockets for more ROMs/EPROMs and maybe EEPROMs if a modern version. But obviously are more expensive.

Mark

[Becky]

The DIY route sounds like an option. I've built a Spectrum clone from a bare board, so a couple of wires isn't so scary. I read something earlier which involved cutting tracks on the PCB, that was what I didn't fancy. The ROM/RAM boards look good, but are out of my price range at this time. What is the biggest capacity of SRAM that can be used?

Edit: Penny dropped about the EEPROM. that sounds interesting. Can that be written to inside the machine?

[MartinB]

Edit: Penny dropped about the EEPROM. that sounds interesting. Can that be written to inside the machine?

There are some utilities here for in-machine EEPROM writing and management - I don't know if there are any others around?

[Bobbi]

There is a BASIC program from BooBip for programming the EEPROM in the machine too ... http://www.boobip.com/software

[MartinB]

That looks better than my shambles - I never claimed to be a software ninja....

[1024MAK]

What is the biggest capacity of SRAM that can be used?

Err, you don’t really want to worry too much about that. The most practical method is to use a 32k byte SRAM chip, that then gives you TWO 16k byte sideways RAM ‘slots’ (banks). That’s enough for most games or to use for ROM files loaded from mass storage.

Edit: Penny dropped about the EEPROM. that sounds interesting. Can that be written to inside the machine?

Yes. Martin has already given a link to his err, comprehensive topic! (Plenty of bedtime reading there!)

Mark

[SteveF]

It's worth noting that although EEPROM can be written to in the machine, it isn't writeable in the same way as sideways RAM - so games which can use sideways RAM as extra memory won't be able to take advantage of EEPROM as an alternative. So it's good to have both.

[KenLowe]

Or better still, get some FRAM. It's non volatile, and can be written to just like RAM. There are some caveats, though. The 5V version is only available in SMD package, and IIRC some mods are required to the beeb to condition a couple of the control signals. It can be dropped into my IntegraB board without any problem.

[Becky]

I did my Sideways RAM upgrade last week. I followed gadgetuk164's YT video. He used non volatile RAM, but the wiring was the same as the guide on the CD full of goodies that came with my MMC interface. Took a lot of trial and error to get it to work and work out what Banks I had (A + E). I eventually worked out that the program RLOAD doesn't work unless I select the NULL core on the PiTube. (Gave a HEX Error)

Since discovering Beebug's help program, I'm already thinking that I want to upgrade NV rom.

Totally hooked, god I love my Beeb!