EEPROM - the Holy Grail of Sideways Rom?

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MartinB
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EEPROM - the Holy Grail of Sideways Rom?

Postby MartinB » Tue Dec 10, 2013 7:51 am

As per the title, a drop-in sideways rom chip that you can program and erase in your Acorn without the need for a separate programmer and eraser, set and unset write protect without the need for switches and finally, fully non-volatile without the need for batteries? Yes, it is possible :D

Pictures, words etc. - I feel another Shaky-Cam production coming on....



I need to do some more work on a Beeb (timing issues) so don't rush out and buy any just yet (I have a fair few btw and not too bad a price at CPC) but lookin' promising 8)

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby flaxcottage » Tue Dec 10, 2013 8:09 am

=D> =D> =D> =D> =D> =D>
- John

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby danielj » Tue Dec 10, 2013 8:32 am

Oooh, you're good. =D>

d.

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby paulv » Tue Dec 10, 2013 8:42 am

Clever :D =D>

I knew you were working on something. The reveal was worth the wait :D

Paul

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby 1024MAK » Tue Dec 10, 2013 9:43 am

flaxcottage wrote: =D> =D> =D> =D> =D> =D>
danielj wrote:Oooh, you're good. =D>
paulv wrote:Clever :D =D>

I knew you were working on something. The reveal was worth the wait :D
Err, what they said ^^^.... :lol: =D>

Mark
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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby s1paulr » Tue Dec 10, 2013 10:29 am

Very very nice =D>

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby station240 » Tue Dec 10, 2013 10:31 am

Let me guess, the timing issues are due to the beeb being too fast, something the Electron 'solves'

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby sweh » Tue Dec 10, 2013 1:21 pm

MartinB wrote:As per the title, a drop-in sideways rom chip that you can program and erase in your Acorn without the need for a separate programmer and eraser, set and unset write protect without the need for switches and finally, fully non-volatile without the need for batteries? Yes, it is possible :D

Yeah, the advantage of EEPROMs is that they typically come in the same package as an EPROM and so are plug-in compatible. Flash chips (eg the sort used in the IFEL RAM/ROM board) have many of these advantages but would likely need a carrier board.
Rgds
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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby MartinB » Tue Dec 10, 2013 1:40 pm

Thanks for the encouragement as usual folks 8)

I have actually spent quite a long time on this one way or another because there were quite a few conundrums to solve. A good example is using the device in an application where a 32k chip can't be fully accessed such as in the Beeb where, without performing machine hardware mods (which is a no no I feel [-X), only 16k devices are supported. The reason this is an issue beyond the usual tying of A14 high (or low) is because to use the eeprom built-in lock, unlock and erase covert sequences, you have to able to write a special sequence to one byte in the upper 16k and one byte in the lower 16k. This isn't a big problem in the case of EUP because it caters for 32k chips by design and we can switch rom bank id's to access the necessary addresses but for the Beeb, with only 16k slots, a bit of innovation is required. The solution in the end was actually quite elegant, just isolate A14 on the chip and tie it to it's own A12 - this partitions the 32k into alternate active blocks encompassing the 'magic' addresses but still looking like a contiguous 16k to the Beeb. You only get to use 16k of the device but it does allow all the intelligent functions to be used. Simple really!

station240 wrote:Let me guess, the timing issues are due to the beeb being too fast, something the Electron 'solves'
No, I don't think it's a speed issue as such because remember, the Elk still runs at 2MHz when accessing rom and so is the same speed as the Beeb in this application. I need to do some more characterisation on the Beeb but it looks like it might be related to the continuous heartbeat on nOE of the sideways rom sockets not aligning well with the eeprom's expectations.

Anyway, it's a work in progress on the Beeb but I think the Elk software is pretty much sorted - I just need to check the non-32k applications such as the Rombox+ and in writeable cartridges. (Which reminds me, when used in a vanilla Beeb, we do need to add a flying lead and clip to the eeprom to pick up RnW which isn't available on the rom sockets.)

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby Advance » Tue Dec 10, 2013 3:22 pm

Well done yet again, Mr. B.
As Paul said, not exactly a surprise to learn you have been beavering away but I'd never have guessed the outcome.
Looks like it's time I got around to doing t'other Martin's zif and switch mod to the EUP board.
Good luck with the final stages.

Hugh
PS: This is what the trendy butch Beebist is wearing today.
ae235.jpg

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby MartinB » Tue Dec 10, 2013 7:31 pm

Well Hugh, whilst 'tis the season to be jolly, 'tis also the season when it's feckin' freezing in my Beeb cellar..... :wink:

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby CMcDougall » Tue Dec 10, 2013 8:02 pm

Great work Martin!!! =D> =D> =D>

glad you are keeping to the elk, as some 'hints' on your new mission/s
were pointing at Arc's (pffft), so 8)

absolute magic with no physical switches hanging out at the back of elk/plus1 \:D/ and no leaking battery >20yrs :)
season when it's feckin' freezing in my Beeb cellar

taken a leaf out my book I see, jumpers/coats are cheaper than those greedy heat/light suppliers :x

Col. :D
ImageImageImage

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby davidb » Tue Dec 10, 2013 9:34 pm

Looking good! The project, not the gloves... :lol:

I thought of doing something like this with my pending hardware project, either as a last resort if I can't program the flash ROMs from a microcontroller, or just as additional functionality if/when I finally get a cartridge made. Looking at the Atmel 28C256 datasheet, the command sequences certainly look familiar. You make it look so easy. :)

If you want to test a 32K ROM, you could try the cartridge version of Jungle Journey. It's available from the Downloads section of the Jungle Journey page.

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby MartinB » Tue Dec 10, 2013 10:24 pm

David wrote:You make it look so easy. :)
Heh - thanks but the software isn't too difficult once you get your head around how E2 behaves in practice. Simplistically, if you just allow about 12ms per byte-write, you'd get away with a simple dumb delay loop and could program 16k in around 200s or just over 3 minutes. (For interest, I've looked carefully at the timings and the actual time needed per byte-write varies, plus or minus a couple of milliseconds, depending on how much the byte is changing and the delta in the addresses.) However, I'm employing a fully intelligent algorithm with 64-byte page writes and data polling which massively increases the programming efficiency and completes a 16k worst-case image in mere seconds, the slowest part being the Elk screen address update! Using page writes, you really do need to do a second-pass verify but again, the only sluggish aspect of this is the screen writing. My utils do also have parsers and rom/ram/eeprom detection with validation etc. so as usual, it's not the actual business end of the code that tends to be difficult, it's the proper user interface and error-trapped packaging that takes the time.
and wrote:...the command sequences certainly look familiar.
Yes, they're pretty straightforward and as I alluded to earlier, the tricky part here proved to be the need to access both the upper and lower 16k (device addresses $5555 and $2AAA) when you have the 32k chip plugged into a 16k socket and of course the latter is the prevalent case on Acorn kit. This is where my eureka trick of connecting A14 to A12 ended days of head-scratching misery :D
Of course, my own EUP proved to be a godsend in the first instance because it natively supports full 32k 62256-format devices (as 2 x 16k) and so I was able to characterise the E2 and develop my code in relative technical comfort.
and also wrote:If you want to test a 32K ROM, you could try the cartridge version of Jungle Journey. It's available from the Downloads section of the Jungle Journey page.
Perfect David :D =D>
There's very little stable Elk rom software out there so this will be great - I'm on it........ :wink:

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby sweh » Wed Dec 11, 2013 3:47 am

MartinB wrote:However, I'm employing a fully intelligent algorithm with 64-byte page writes

Do any compatible EEPROMS _not_ support page writes? (I've always found 64 bytes odd for a something like the 28128, 16K*8)

Curious; what EEPROM are you proposing? 28128 and 28256's can't be too easy to find, these days...
Rgds
Stephen

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby MartinB » Wed Dec 11, 2013 7:41 am

sweh wrote:Do any compatible EEPROMS _not_ support page writes?
They may well do, I haven't researched every chip out there - I'm not sure of the point of your question though? :-k
and wrote:(I've always found 64 bytes odd for a something like the 28128, 16K*8)
Again, not sure what you mean but any page buffer, in this case 64 bytes, has to be implemented within the chip architecture alongside the E2 memory so they don't have free reign. 64 is therefore a reasonably high number in this respect and well serves it's purpose because as you can see from my rough numbers, using page writes divides the programming time by nearly 64.
and wrote:Curious; what EEPROM are you proposing? 28128 and 28256's can't be too easy to find, these days...
Heh - You need to pay attention Stephen, I did say on the video and if you look three posts up, David B has already been on the datasheet case :wink:

Anyway, I have various types but the device I'm currently using is an Atmel AT28C256 and one of my reasons for settling on this is the very reason that they do still seem to be around to buy. On a quick previous check, they're in stock at CPC/Farnell and RS and if I recall, the former are declaring something well over a thousand and RS about 400. On that basis, I suspect there'll be many other suppliers with stock so if the idea proves to be a goer, getting hold of one shouldn't be a problem. (They tend to be on eBay too but usually [not always mind] at inflated prices.)

The only reason I'm not pro-actively pushing a particular device is because I've not finished testing yet and I need to be sure it works as required in the sideways rom role before anyone spends any money. (As I said earlier, I myself have about 8-10 fully tested spare pulls that I could pass on for say a fiver posted but again, not until I'm sure we're good to go with this.)

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby sweh » Wed Dec 11, 2013 12:16 pm

MartinB wrote:
sweh wrote:Do any compatible EEPROMS _not_ support page writes?
They may well do, I haven't researched every chip out there - I'm not sure of the point of your question though? :-k

Just in anyone else is gonna follow in your footsteps are there any devices they need to be aware of that won't be able to make use of the buffer speed advantage.
and wrote:(I've always found 64 bytes odd for a something like the 28128, 16K*8)
Again, not sure what you mean but any page buffer, in this case 64 bytes, has to be implemented within the chip architecture alongside the E2 memory so they don't have free reign. 64 is therefore a reasonably high number in this respect and well serves it's purpose because as you can see from my rough numbers, using page writes divides the programming time by nearly 64.

It was an aside and odd musing; no point. Just "64" seems an odd number; 512bits, 6 address lines... odd numbers :-)
and wrote:Curious; what EEPROM are you proposing? 28128 and 28256's can't be too easy to find, these days...
Heh - You need to pay attention Stephen, I did say on the video

I tend to not watch videos, especially if I'm reading the forum from work :-)
AT28C256 and one of my reasons for settling on this is the very reason that they do still seem to be around to buy.

Ah, good. I'm surprised; there's more of those around than I expected! And pretty cheap as well (from $6->$10 depending on where I look). Not bad :-)
Rgds
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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby mga1103 » Wed Dec 11, 2013 11:32 pm

Nice one Martin! =D>

Good to see you're back in the software development seat again :wink: .

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby 1024MAK » Wed Dec 11, 2013 11:38 pm

I don't know, you wait months for a Martin to come along, and them two turn up in a matter of days :lol:

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby BBCB+64K » Thu Dec 12, 2013 2:29 pm

Wow, this project would be very handy for me since I can't program EPROMs very easily and have to rely on other people to physically swap them over in my Beebs.

Would this work in a BBC B+ with the 32k rom link set?

Keep up the good work Mr. B =D>

Steve
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BBC B+ 128k with external DataCentre with 2GB CF Card, 64MB ARM7TDMI Co-Processor and BeebOPL.

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby 1024MAK » Thu Dec 12, 2013 2:41 pm

Actually, that brings me to another question...

Martin, will your software include the option of working with a model B that has been modified to accept 32k EPROMs in one (or more) of the standard ROM sockets? Of course, said chips are accessed as two 16k banks and depending on how the modification has been done, the ROM numbers vary...

<For those thinking of using an EEPROM in such a machine, don't forget the EEPROM would still need a flying lead for the /WE signal>.

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby sweh » Thu Dec 12, 2013 6:34 pm

MartinB wrote:need to access both the upper and lower 16k (device addresses $5555 and $2AAA) when you have the 32k chip plugged into a 16k socket and of course the latter is the prevalent case on Acorn kit. This is where my eureka trick of connecting A14 to A12 ended days of head-scratching misery :D

So since I had a few minutes I tried to work out why this worked...

For 2AAA, A14=0, A13=1, A12=0
For 5555, A14=1, A13=0, A12=1

Now it becomes clear. By typing A14 to A12 the magic address changes from 5555 to 1555. (I guess the two locations are now &AAAA and &9555 when it's plugged into a SWR slot).

Clever!

Heh, memory is no longer contiguous but it doesn't matter :-) That was something I realised when playing with NVRAM on the Mhz bus; the exact order of the A and D lines to the chip didn't really matter because read and write will assert the lines consistently so who cares if I actually store "128" when I ask to store "1"; it'll still read back as "1" to the Beeb :-)

I'm definitely learning a lot from you guys. Thanks!
Rgds
Stephen

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby sweh » Thu Dec 12, 2013 6:59 pm

1024MAK wrote:Martin, will your software include the option of working with a model B that has been modified to accept 32k EPROMs in one (or more) of the standard ROM sockets? Of course, said chips are accessed as two 16k banks and depending on how the modification has been done, the ROM numbers vary...

I'm gonna make a guess, here... it'll be a good test to see whether I understand what Martin has done :-)

If you modify the EEPROM as he suggests then you'll have a 16K EEPROM that will work with his software unchanged. If, however, you don't modify the EEPROM then you'll be able to access all 32K but the magic addresses will change; you'd need to page in one ROM (&FE30=bank1) and write to &AAAA and then page in the other ROM (&FE30=bank2) and write to &9555 to enable write access. At that point you can do the 64 byte page writes (remember to page in the bank you want to modify).
Rgds
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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby jgharston » Thu Dec 12, 2013 7:25 pm

MartinB wrote:I need to do some more work on a Beeb (timing issues) so don't rush out and buy any just yet (I have a fair few btw and not too bad a price at CPC) but lookin' promising 8)
What code are you using to write to the EEPROM?

Code: Select all

$ bbcbasic
PDP11 BBC BASIC IV Version 0.25
(C) Copyright J.G.Harston 1989,2005-2015
>_

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby MartinB » Thu Dec 12, 2013 8:22 pm

Exactly as you have figured Stephen - I have actually got two versions of the lock/unlock/erase configure program called EEP16 and EEP32 where the former assumes the A14/A12 link is in place creating a 16k device and the latter assumes both 16k banks are available in two consecutive rom slots. In both cases, the magic addresses are always $9555 and $AAAA but for EEP32, rom bank switching is required.

Jonathan - just some simple assembler utils I have written myself.

On the Elk, writing to the E2 is fine and is 100% reliable but I seem to have some intermittent read problems. On the Beeb however, writing is the bigger problem. I'm still looking at the behaviours (just a bit strapped for time like everyone) but hopefully can sort it because I think this device would be really useful in our world.

Still don't go out and buy any just yet though people in case I find an unworkable problem. Hopefully not but can't be sure yet..... :-k

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby MartinB » Thu Dec 12, 2013 10:58 pm

Ok people, I now know why read problems have been occurring on the Elk and whilst I still need to fully quantify and understand the event, the fix is very easy but it does mean that I have to go back on one of the promised features of the Holy Grail #-o

If an E2 prom believes it has been written to, after about 100us it enters it's hard-write cycle for the target address(es) which typically takes about 10ms. Of particular note, it follows this process even if it soft-locked (write-protected) but, if it is locked, the hard-write will of course be unsuccessful. Most importantly here, whilst the device is in the hard-write cycle, the prom won't yield any valid read data, only data polling ring-backs. In summary then, if you write to an eeprom, even if it is locked, it becomes unavailable for around 10ms.

Now, what seems to be happening on the Elk (and I very much suspect this is the Beeb issue too but perhaps a slightly different manifestation) is that the timing regime of nCS, nOE and RnW are somehow allowing occasional false writes to reach the device causing it to go offline for a short period but this short period might as well be years in computer terms!

So, without even needing to fully quantify these spurious writes, I can prove the theory and fix the problem by the addition of a write-protect switch. Even though one is not needed to stop the device being illegally corrupted, (this of course is done by the soft-lock), we do appear to need one on an Elk (at least) to prevent spurious writes from occasionally disabling the chip. (I should point out that this also occurs when using the Rombox+ rom slots so it's not an EUP issue before anyone asks!)

Prior to this discovery, David B's 32k rom version of Jungle Journey ( =D> ) wouldn't run from the e-squared. However, having bunged a write-protect switch onto my EUP, all is well. Watch the video and look out for the slight-of-hand during the Elk re-cycle..... :wink:



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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby davidb » Thu Dec 12, 2013 11:16 pm

Nice work! =D>

I suppose that you loaded the ROMs into low priority ROM banks given that the Electron didn't boot up directly into the game.

You say that Jungle Journey wouldn't run initially. Is it spuriously writing to the ROM? I thought I'd removed any writes back to program memory, but it might be worth checking.

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby MartinB » Thu Dec 12, 2013 11:22 pm

No, I haven't checked David but it's not exclusively Jungle that I've seen problems with. Some roms appeared to run fine but others, particularly those which batter the rom access such as UPURS, also seemed to occasionally hiccup. I'm pretty sure it's nW unintentionally bleeding into a nCS cycle every now and then.

The E2 is in rom slots 2 and 3 in EUP - should that cause Jungle to auto-boot?

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby davidb » Thu Dec 12, 2013 11:39 pm

According to Application Note 15:
Acorn Plus 1 priority is forced as follows, highest priority first:
15 to 12
7 to 0
BASIC
This means that if sideways ROMs are used with the Plus 1 fitted then a language in 0 to 7 will power-up
ahead of BASIC.

I think the ROMs are service ROMs, so it looks like I should probably update the instructions to tell users to use the *JUNGLE command to play the game.

In hindsight, this is probably for the best because you'd have a hard time rewriting the EEPROM if the game started every time you switched the Electron on. :)

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby MartinB » Sat Dec 14, 2013 11:50 pm

I thought I might as well capture some snaps of the nW versus nCS_Read conflict on the Elk, so I tacked a couple of wires onto the back of the PCB, hung the scope on and started looking. Guess what - yep, with a scope probe on RnW at the EEPROM, the problem goes away #-o. I've seen such things before and basically this confirms what I thought about the issue most likely being caused by a sloppy signal edge rather than anything major. David's Jungle Journey roms proved to be really useful here because after loading them into the e-squared banks, typing *JUNGLE without write protect just bombs the Elk whereas typing *JUNGLE with write protect set true fires up the game perfectly. (Note that the roms don't corrupt because of the e-squared soft-lock option - when a false write is triggered, the e-squared just pouts for 10ms before returning with a smile.)

Therefore, the Elk conclusion is that everything is as I promised except that you do need to have a write protect switch. Not to prevent corruption, but to prevent seemingly yet another quirk of the Plus 1 (some? all? mine? yours?) from occasionally garbling reads with a lazy write edge :roll:

So....

1. Does the fact that a switch is needed on the Elk still make E2 a palatable non-volatile sideways storage option for folk? (It is otherwise as good as I have described.)

2. I'm pretty certain I can sort the Beeb problem because after a bit more playing, I'm sure it's as I previously surmised and related to the inherent regular strobing of nOE. I think I will try a second flying lead and take the isolated e-squared nOE to WnR as I did on EUP. The Beeb solution then would potentially be two shorted pins on the e-squared chip with two clip-on flying leads plus, possibly, a write protect switch as per the Elk but that's not a given just yet. (Whatever I find, if it involves even a sniff of hardware mods to the Beeb then it's just not happening [-( )

3. To save me digging, does anyone know how to disable the 100Hz polling call to roms on the Elk? It's a real pain in the butt when you're investigating rom access issues. Maybe there's a OSBYTE (FX) call or something? (The 100Hz call is also implemented on the Master btw.)


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