Sideways RAM on the BBC Micro

for bbc micro/electron hardware, peripherals & programming issues (NOT emulators!)
BitSeeker
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Sideways RAM on the BBC Micro

Postby BitSeeker » Fri Mar 30, 2018 8:37 pm

On the back of another topic I came across some information about loading ROMs into sideways RAM, which seems a more flexible way of doing things than adding chips to the ROM slots. Having done a little bit of research I see that this is an additional amount of RAM memory that can occupy a ROM slot. However I have so far found very little information on how to add this memory. I did find this:
http://www.retroclinic.com/acorn/swr/swr.htm
However I don't like the idea of messing with this vintage machine by cutting tracks etc. Is this the only way? I also could not find the RAM chips being referred to.

I am hoping that there are other resources that discuss this topic and provide some advice on the hardware. If anyone can point me in the right direction it would be appreciated.

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Re: Sideways RAM on the BBC Micro

Postby CMcDougall » Fri Mar 30, 2018 8:45 pm

there is Much easier ones than that, no solder /hacks required
viewtopic.php?f=8&t=12946#p167240

info:
http://www.boobip.com/hardware
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Re: Sideways RAM on the BBC Micro

Postby BitSeeker » Fri Mar 30, 2018 8:49 pm

Would love one of those! If only I could PM.....

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Re: Sideways RAM on the BBC Micro

Postby CMcDougall » Fri Mar 30, 2018 8:52 pm

now updated link for direct above.
he has none on eBay at mo.... but get discount so no ebay fees.
DONT use the other ones on eBay, he just steals everything from this very forum & upsets mature members bigtime [-X
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Re: Sideways RAM on the BBC Micro

Postby cmorley » Fri Mar 30, 2018 9:13 pm

I'm the BooBip guy. Please feel free to ask me any questions. The forum moderators can enable PM for you or you can email me (address is on the website CMcDougall linked :) ).

EEPROM is the best option for loading ROMs. They program in seconds and retain the last thing you programmed. Sideways RAM is less useful for ROMs but works with some games (e.g. Exile on a B) to get better graphics & sound.

I'm not a fan of cutting tracks on the old computers - which is why I designed my modules the way I did. You can take them out, remove the spring clips and you're back to factory spec. Quite a few forum members have my modules - let them speak for how good/easy to fit they are. (Mr.McDougall your cheque is in the post ;) )

Chris

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Re: Sideways RAM on the BBC Micro

Postby sydney » Fri Mar 30, 2018 9:57 pm

BitSeeker wrote:Would love one of those! If only I could PM.....


PMs enabled.

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Re: Sideways RAM on the BBC Micro

Postby BitSeeker » Fri Mar 30, 2018 9:58 pm

Chris, thanks for your post and link to your website. I had to look up the term EEPROM (as opposed to EPROM) as I wasn't familiar with that device. Given that this retains memory on switch-off this does sound like a better solution than RAM. I take it that as it is programmed "in-circuit" it does not require a separate programmer, like the original EPROM devices? Could I also ask whether it is possible to have more than one in a machine?

I also came across this device:
https://www.ebay.co.uk/itm/Acorn-BBC-Mi ... 3173979647
What I don't get is why the 'flash memory" requires a battery backup? It is twice as expensive but does provides a fully populated solution. I am mulling it over and will probably e-mail you in the next day or two.

Looks like the admins have enabled PMs on my account as well. Thanks sydney.

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Re: Sideways RAM on the BBC Micro

Postby cmorley » Fri Mar 30, 2018 10:18 pm

BitSeeker wrote:Chris, thanks for your post and link to your website. I had to look up the term EEPROM (as opposed to EPROM) as I wasn't familiar with that device. Given that this retains memory on switch-off this does sound like a better solution than RAM. I take it that as it is programmed "in-circuit" it does not require a separate programmer, like the original EPROM devices? Could I also ask whether it is possible to have more than one in a machine?.


Yes it programs in the machine. It ships with the programming tool preinstalled. Yes you can fit more than one. Mix and match with original ROMs & my other modules.

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Re: Sideways RAM on the BBC Micro

Postby KenLowe » Fri Mar 30, 2018 10:51 pm

BitSeeker wrote:I also came across this device:
https://www.ebay.co.uk/itm/Acorn-BBC-Mi ... 3173979647
What I don't get is why the 'flash memory" requires a battery backup? It is twice as expensive but does provides a fully populated solution.

That is also a very good board. It effectively provides 8 x 16k EEPROM banks and 8 x 16K SWRAM banks. The battery is to provide backup to the SWRAM banks. Having SWRAM on your computer can be very handy, as it can be used as additional storage by several games. Also, if you want to use MMFS (modern disk emulation solution), then you can load the ROM into a SWRAM bank, and it will dynamically use some of the SWRAM memory keeping PAGE at &E00 (instead of &1900). This frees up main memory for other uses, whilst still being able to load and save to 'disk'. The board is very easy to install and is of good quality, requiring only a single jumper wire to be connected to one of the jumpers on the main board. However, it can be quite difficult to remember how all the memory is laid out (which banks are EEPROM, which are RAM, and which are write protected RAM).

Another 'fully populated' solution is the RAM / ROM board built by kjell: http://www.sundby.com/index.php/bbc-micro-ramrom/. It also works very well, but I had to make a critical modification to allow flashing from the BBC. See this post: viewtopic.php?f=3&t=13198&p=171796&hilit=eeprom#p172751. It also required 6 clips to be connected to the legs of various ICs on the main BBC board (assuming you don't want to solder wires to the legs of ICs). Some of these ICs are underneath the keyboard, making it quite difficult to keep them in place when the keyboard is secured down in position. Also, the position of the 6 pin header on the board is not great either. When you attach the ribbon cable to the header, it again makes it difficult to secure down the keyboard. I removed the header on my board, and replaced it with a 90Deg header, which solved this problem for me. It works well, but is not quite such a robust solution as the other 'fully populated' board. This board also doesn't provide battery backup for the SWRAM.

I believe Boobip also offers a non battery backed SWRAM solution that will work in conjunction with his EEPROM board.

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Re: Sideways RAM on the BBC Micro

Postby flaxcottage » Sat Mar 31, 2018 9:53 am

From years of experience of using various sideways RAM boards, extension ROM boards I have concluded;

1. modern variants are far better than 'authentic' retro ones - they are quicker to use and consume less power,

2. there is a need for both sideways RAM and extra ROMs - some very useful ROMs come on carrier boards squeezing up to 128K into a single 16K footprint,

3. for the BBC micro then the BooBip ones are the best I have used. If using an 8271 DFS loading SWR images is a little fiddly compared to a 1770 DFS which can use the in-built *SRLOAD command. A BBC micro with MMFS and 1770 DFS installed can be set up to load SWR from Shift-Break incredibly easily. This really is the bee's knees. The BooBip EEPROM board is fantastic and so simple to use and is non-volatile. A disadvantage for users with Beebs which are mobile is that the flying lead clips may become dislodged during transit.

4. for the 64K BBC B+ the method of piggy-backing 3x32K static RAM chips in one ROM/RAM socket provides the most versatile user experience. This leaves 4x16/32K ROM sockets on the main board. I use a Mega3 ROM in one, Interbase in another then have 2x32EPROMs in the others programmed with my 'must have' ROMs. The B+ also has an MMC card fitted and can load images into up to 6xSWR banks from Shift-Break.

If you have a 128K B+ you will lose 32 SWR but gain another 16/32K ROM socket.

5. The Master already comes with 4x16K SWR banks built in, one internal 16K ROM and two cartridge slots to hold 4xROMs. To improve its versatility I have installed an updated OS (this was the Retroclinic variant which is switchable between OS types and includes Y2K compatibility; it also has a Datacentre driving capability), an internal Datacentre and CF-card, ADFS providing 4x500Mb HDD. One of the cartridge slots permanently holds ANFS and Exmon II. The other slot contains an IFEL master RAM/ROM board. This contains up to 8xROM image slots which are battery backed and so non-volatile. Pairs of images can be switched in or out for different purposes. The IFEL board is extremely versatile and is far better than the switched ROM cartridges that were available BITD. It is even possible to have a custom OS programmed replacing some of the useless software that comes included in the Master OS ROM.

A Master and a Datacentre or a Beeb and an MMC interface are marriages made in heaven! :D
- John

Why do I keep collecting Acorn gear? I'm going to need a considerably bigger man-cave. :?

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Re: Sideways RAM on the BBC Micro

Postby KenLowe » Sat Mar 31, 2018 10:32 am

flaxcottage wrote:2. there is a need for both sideways RAM and extra ROMs - some very useful ROMs come on carrier boards squeezing up to 128K into a single 16K footprint

I'm not trying to push them at all, but for completeness, the two boards I referenced above allow you to use the ROM slots on the main board, thereby still allowing the use of GoSDC and other ROMs on carrier boards (eg Spellmaster 128k) - obviously you lose access to some of the onboard EEPROM space when you've set it up this way.

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Re: Sideways RAM on the BBC Micro

Postby BitSeeker » Sat Mar 31, 2018 3:25 pm

Thanks for all the helpful information which I now need to consider.

In the meantime, is it possible to upgrade the BBC Micro from 32k to 64k RAM? Is there any advantage in doing so? I'm not sure whether there is a difference between this and putting sideways RAM into ROM slots, so my apologies if I am going over exiting ground again.

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Re: Sideways RAM on the BBC Micro

Postby 1024MAK » Sat Mar 31, 2018 4:07 pm

BitSeeker wrote:Thanks for all the helpful information which I now need to consider.

In the meantime, is it possible to upgrade the BBC Micro from 32k to 64k RAM? Is there any advantage in doing so? I'm not sure whether there is a difference between this and putting sideways RAM into ROM slots, so my apologies if I am going over exiting ground again.


Yes and no...!

In a BBC B, half the memory is main RAM (0x0000 to 0x7FFF). Next is the sideways 'ROM' area (16k bytes) where either BASIC, or a number of other sideways ROMs, EPROMs, EEPROMS, Flash or RAM can reside (0x8000 to 0xBFFF). Next up is the OS ROM (0xC000 to 0xFFFF). That completes the memory that the CPU can address.

However, in the B+, the B+128 and the various Master machines, there is additional RAM called shadow RAM. This covers the same address range as the main RAM. The advantage for compatible programs, is that the program and it's data does not have to share RAM with the screen data. As the screen can take up to 20k bytes of memory, that means the program and it's data gets an extra 20k bytes of main RAM.

Years ago expansion boards were available for the BBC B to add shadow RAM. But they don't come up for sale very often.

However, most games were not written to take advantage of shadow RAM :(

For more on sideways ROM and sideways RAM, have a look at this web side :wink:

Mark
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Re: Sideways RAM on the BBC Micro

Postby BigEd » Sat Mar 31, 2018 5:00 pm

It's good to have all these terms and possibilities explained... in fact I'm half inclined to buy one or two of the modern offerings for my own Beeb, if it weren't for the fact that my Master already has a lot of goodies built-in.

Might be a good time to note that a 6502 second processor will also give you 64k of extra memory, in a way which is excellent for application programs and Basic, but rarely taken advantage of by games. An original cheese-wedge will be expensive, but a Raspberry-pi based one is not.

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Re: Sideways RAM on the BBC Micro

Postby BitSeeker » Sun Apr 01, 2018 12:49 pm

From memory, I had thought that the BBC B (as well as C64 , Spectrum an other 8bit machines) could address only 64k of memory. However seeing a reference to a B+128 I started to wonder whether it can address 128k, but evidently it seems it cannot, except my memory page swapping tricks. Then there is also the question of what software has support for such enhanced configurations, so it is interesting to note that most games do not support shadow memory.

I have seen a "cheese wedge" for sale but it came with BBC Micro, monitor and other bits and the seller wanted £500 for the lot which seems a very expensive way of getting one, so the Raspberry PI idea is of interest. I didn't realize that was possible!

Thanks for the various links to more information on this subject. All have been very helpful.

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Re: Sideways RAM on the BBC Micro

Postby BigEd » Sun Apr 01, 2018 1:08 pm

Yes, most 8 bit micros will only deal with 16 bit addresses, which is a limit of 64k on the addressable memory. Beyond that you have to have some kind of banking or paging. Some machines offer a tidy solution and some offer an untidy solution! Acorn's solution in the Beeb of sideways ROM banks is pretty good for its purpose: applications installed as ROM, not very large, using RAM in the obvious way. Beyond that, when you have sideways RAM, it's a bit less easy to use, and lacking a standard it is difficult for software to take advantage of it. But it works well for loading ROMs temporarily.

The shadow RAM was a nice idea, affecting only the video memory and giving a larger free space to applications. I don't know how compatible the various shadow RAM efforts are with each other - is the B+ just like the Master, or only somewhat like it? Hopefully for the application it doesn't matter, they just see a nice high value of HIMEM.

By far the cleanest environment for large memory is the second processor - which was always on the cards and was, I think, introduced fairly early on. Early '84 apparently. An application gets something like 62k of space to exist in, and Basic programs have 44k when running HiBasic.

That said, there is BAS128, a Basic which makes use of four sideways RAM banks and offers 64k for the Basic program and data, at the cost of some performance.

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Re: Sideways RAM on the BBC Micro

Postby flaxcottage » Sun Apr 01, 2018 1:42 pm

The Beeb is what it is - an amazingly versatile 8-bit computer.

If you want more programming memory get a Raspberry Pi zero. It costs about £4-5 and with RISCOS pico installed it gives an insane amount of memory for BASIC. :D
- John

Why do I keep collecting Acorn gear? I'm going to need a considerably bigger man-cave. :?

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Re: Sideways RAM on the BBC Micro

Postby BigEd » Sun Apr 01, 2018 2:20 pm

Or hook up the same Pi with an adaptor, as a second processor, and run Basic in Native ARM mode: not quite so much memory, not quite the same Basic, not quite the same video modes, but a real Beeb as a front end!

(I'm a big fan of RISC OS Pico though.)

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Re: Sideways RAM on the BBC Micro

Postby crj » Sun Apr 01, 2018 3:54 pm

cmorley wrote:I'm the BooBip guy. Please feel free to ask me any questions.

OK. Since this thread is talking about EEPROM v. RAM... have you considered making a variant of your boards with a 64K F-RAM on it? I mean, such a board would cost a tenner more than your other offerings, but has all the advantages of both RAM and EEPROM without the need for a battery.

(Ideally, there would be a hardware read-protect switch, for when you screw up bigtime. Though booting with it unplugged then plugging it back in so you could wipe it would be an option.)

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Re: Sideways RAM on the BBC Micro

Postby cmorley » Sun Apr 01, 2018 4:09 pm

crj wrote:
cmorley wrote:I'm the BooBip guy. Please feel free to ask me any questions.

OK. Since this thread is talking about EEPROM v. RAM... have you considered making a variant of your boards with a 64K F-RAM on it? I mean, such a board would cost a tenner more than your other offerings, but has all the advantages of both RAM and EEPROM without the need for a battery.

(Ideally, there would be a hardware read-protect switch, for when you screw up bigtime. Though booting with it unplugged then plugging it back in so you could wipe it would be an option.)


Never considered it. The chip you've linked is 64kbit so 8kx8. The largest parallel FRAM mouser sell is 32kx8 @ £10.60+VAT... so you'd need 2 to get 4x16KB banks. I don't think anyone would buy that it is just too expensive.

I suppose there is a benefit for E00 ADFS or SWRAM MMFS etc so you don't have to load SRAM every time you power on the machine.

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Re: Sideways RAM on the BBC Micro

Postby RobC » Sun Apr 01, 2018 4:15 pm

cmorley wrote:I suppose there is a benefit for E00 ADFS or SWRAM MMFS etc so you don't have to load SRAM every time you power on the machine.

I use these in a couple of my machines to hold DFSE00 and ADFSE00:
https://datasheets.maximintegrated.com/en/ds/DS1230AB-DS1230Y.pdf

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Re: Sideways RAM on the BBC Micro

Postby BitSeeker » Sun Apr 01, 2018 6:36 pm

It seems to me that an EPROM programmer might be handy. Anyone know whether a Stag PP28 EPROM and EEPROM programmer would be suitable to program EPROMs for the BBC? I have spent some time trying to figure out which EPROM types this will do and which the Beeb will take and am still unsure. Alternatively, would I be better off buying one of those cheap programmers from China?

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Re: Sideways RAM on the BBC Micro

Postby BigEd » Sun Apr 01, 2018 6:44 pm

(See the earlier discussion: EEPROM, RAM, and battery backed RAM are all much more convenient than EPROM. That said, EPROM is very authentic. Don't forget to buy a load of EPROMs and a UV eraser!)

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Re: Sideways RAM on the BBC Micro

Postby BitSeeker » Sun Apr 01, 2018 7:24 pm

Indeed the cost of the EPROM eraser would need to be factored in as well! At cheapest from China, both together at minimum would cost somewhere around £35, before I even purchased any EPROM chips. The cost of EPROM chips would soon mount up. By contrast, the cost of the 16 slot board is £40 and 2 x BooBip boards (1 x 64kb EEPROM + 32kbRAM/ROM kit giving 4xROM and 2xSWRAM) would be £36.50 inc postage. I asked about the Stag because the cost that was not too far off the far east products, but I am considering all options. I paid £50 for the Beeb including postage so either solution would almost double my outlay! The cheapest to fit would be 1 x BooBip EEPROM board at £18. That does give me 4 ROM slots to play with in addition to the 4 that are already filled on the board. I am still trying to weigh up whether 4 additional slots will suffice or whether to go for the 16 slot option. Decisions, decisions...
Last edited by BitSeeker on Mon Apr 02, 2018 9:21 am, edited 3 times in total.

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Re: Sideways RAM on the BBC Micro

Postby BigEd » Sun Apr 01, 2018 7:29 pm

Do you already have in mind which ROMs you might need? I mightn't be typical, but I need hardly any: MMFS and UPURS. There was a previous thread seeking recommendations and anecdotes:
Best ROMs to install on EEPROMs

Which is to say, you might not need that many slots.

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Re: Sideways RAM on the BBC Micro

Postby BitSeeker » Sun Apr 01, 2018 7:37 pm

Well, I was thinking of an assembler/disassembler (Exmon?), but there are also a number of ROMs on the MMC CD. I don't know which of these will be useful at this point. I might also like to try an alternative programming language such as Pascal. Perhaps not that many ROMs initially, but it may also be useful to have some spare slots. I'm thinking a single BooBip board will give me some headroom but I will probably fill two or three of those 4 slots pretty quickly. Whether I will have need for any more slots than that remains to be seen.
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Re: Sideways RAM on the BBC Micro

Postby sydney » Sun Apr 01, 2018 7:59 pm

Thats the beauty of the boobip eeproms - you can simply load the roms you want in a matter of seconds.
Need a disassembler - load exmon, want to program in pascal - load pascal, want to write a letter - load view. Much easier than taking the lid off and swapping an eprom.

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Re: Sideways RAM on the BBC Micro

Postby 1024MAK » Sun Apr 01, 2018 8:41 pm

The BBC B can use 2764 / 27C64 8k byte EPROMs and 27128 / 27C128 16k byte EPROMs as standard. You can also use 27256 / 27C256 32k byte EPROMs, but the Beeb can only see half (the top 16k bytes) of the EPROM. The rest of the EPROM memory is not accessible. With a small modification, it can access all the memory in the chip. With a slightly more complex modification, you can use 27512 / 27C512 64k byte EPROMs.

If you know what applications you want, there are members here who will 'burn' (program) EPROMs for you.

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Re: Sideways RAM on the BBC Micro

Postby crj » Sun Apr 01, 2018 10:16 pm

cmorley wrote:Never considered it. The chip you've linked is 64kbit so 8kx8. The largest parallel FRAM mouser sell is 32kx8 @ £10.60+VAT... so you'd need 2 to get 4x16KB banks. I don't think anyone would buy that it is just too expensive.

OK, I'm an idiot, was in a hurry, and dug out the wrong part. )-8

There are quite a few parallel F-RAM parts to choose from, and the prices per Kbyte get lower as one goes up the range. This one, for example, is 128K*8 for £18.58+VAT singly. Not bad for 8 banks's worth.

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Re: Sideways RAM on the BBC Micro

Postby KenLowe » Sun Apr 01, 2018 10:24 pm

crj wrote:There are quite a few parallel F-RAM parts to choose from, and the prices per Kbyte get lower as one goes up the range. This one, for example, is 128K*8 for £18.58+VAT singly. Not bad for 8 banks's worth.

...and you're now starting to get into the 'fully populated board' territory. Both the boards I've mentioned above have both 128k*8 SRAM, and 128k*8 EEPROM onboard, giving the full 16 banks. One comes in at £30 delivered (Sundby), the other £40 (ebay).