EEPROM - the Holy Grail of Sideways Rom?

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

Postby MartinB » Wed Jul 20, 2016 8:29 pm

Heh heh - that's the ticket Simon... =D>

Thing is, since I called these wretched eeproms the "Holy Grail", people keep popping up with examples of why they clearly aren't... :shock: #-o :lol:

Andy - if you have a DVM, can you (with power off) see if pin 20 on WE sockets 14L and 14H are common, i.e. shorted together. Only if you have a moment...

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby trixster » Wed Jul 20, 2016 8:57 pm

martin, wilco. Now, bearing in mind that im a total moron at anything electrical, using the multimeter's continuity mode, there's no indication (buzzer) to imply that pins 20 on 14H and 14L are shorted. Does that help?
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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby 1024MAK » Wed Jul 20, 2016 9:01 pm

trixster wrote:martin, wilco. Now, bearing in mind that im a total moron at anything electrical, using the multimeter's continuity mode, there's no indication (buzzer) to imply that pins 20 on 14H and 14L are shorted. Does that help?

Interesting. Try using a resistance range (the lowest range, say 20R or 200R or simular). You are looking for less than 10 ohms.

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

Postby MartinB » Wed Jul 20, 2016 9:06 pm

Yes, it means they're not commoned and Plan C won't therefore work! :roll: (Plan C was in my head only... :wink: )

Well, I don't know what to recommend now really. I saw your thought about me borrowing it to remove the write-hijacking and I'd ordinarily be fine with that but Beeb-wise, I'm currently writing cheques that my body can't cash so you'd have to ask me again in a few months if you're still chasing a solution... 8)

(Mark - we overlapped. It's quite possible that they're not common but they equally could have been which would have allowed another test.)

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby trixster » Wed Jul 20, 2016 9:07 pm

Assuming I've done it right, that shows 5.41
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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby trixster » Wed Jul 20, 2016 9:07 pm

1024MAK wrote:
trixster wrote:martin, wilco. Now, bearing in mind that im a total moron at anything electrical, using the multimeter's continuity mode, there's no indication (buzzer) to imply that pins 20 on 14H and 14L are shorted. Does that help?

Interesting. Try using a resistance range (the lowest range, say 20R or 200R or simular). You are looking for less than 10 ohms.

Mark


Assuming I've done it right that shows 5.41

Martin, no worries about trouble shooting the board, I totally understand! Life is busy and beebs are just hobbies after all!
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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby 1024MAK » Thu Jul 21, 2016 3:45 am

trixster wrote:
1024MAK wrote:
trixster wrote:martin, wilco. Now, bearing in mind that im a total moron at anything electrical, using the multimeter's continuity mode, there's no indication (buzzer) to imply that pins 20 on 14H and 14L are shorted. Does that help?

Interesting. Try using a resistance range (the lowest range, say 20R or 200R or simular). You are looking for less than 10 ohms.

Mark


Assuming I've done it right that shows 5.41

That's far more promising. It would be very unusual for the two sockets used for RAM to have different active low Write Enable (/WE) controls.

I'm on nights at the moment (except my body and brain haven't worked that out yet :( ). So will have a think about this (a lot) later today :shock:. As this is my last turn of duty this week :D.

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby MartinB » Thu Jul 21, 2016 5:43 am

Mark wrote:It would be very unusual for the two sockets used for RAM to have different active low Write Enable (/WE) controls.

It would Mark but I asked Andy to check Pin 20 which is /CS (so chip select), not write enable. (I was just pondering how the links might work when splitting the 16k into two sockets so the likelihood was that they wouldn't be common....)

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby 1024MAK » Thu Jul 21, 2016 7:00 am

Whoops, saw WE and my tried brain automatically thought /WE so I didn't look at the pin number :oops: #-o :lol:

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby trixster » Sat Jul 23, 2016 6:19 am

Mark, if you're keen to trouble-shoot this then you're absolutely welcome to take my rom board for testing! :D =D> :o

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

Postby 1024MAK » Sat Jul 23, 2016 1:21 pm

Andy, depends on what you want. If you would like me to take a look, sure, I can do that. However, I don't have much time for hardware tinkering at the moment (or reto computing for that matter, been about 13 days since I last fired up any of my retro computers :( ).
I have a couple of MTX's that are next in the queue for repair work. I may have some time in September, but it could be longer, if you are happy to wait.

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby MartinB » Tue Aug 09, 2016 11:08 pm

Some progress on the Master front, in fact nearly there.... :D

There's a lot of discussion to go with this - I'll duly follow up in due course when I get a little time.... 8)



If you can only see a blank square, it's not my fault :x and you can watch the video here.... Clicky
Last edited by MartinB on Wed Aug 10, 2016 5:51 am, edited 1 time in total.

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby MartinB » Wed Aug 17, 2016 10:44 pm

Now my video-embedding anger-spike has died down and I have a little time, the story can continue.... :wink:

I originally assumed that the subject AT28C256 device would function in a Master rom socket exactly as it does in a Beeb B because every other time I've tinkered with sideways ram/rom projects, that assumption has held true. With that in mind, you will recall that I published the following schematic further up the thread...

Image

...but it seems I did so without actually testing on a Master (or if I did, it was a pretty rubbish test ) and basically, as discovered by others and subsequently confirmed by me, it doesn't work... #-o :oops: :roll:

So, more recently, I brought a Master up to full serviceability (mine had all previously failed in one way or another) and I've spent a good deal of time trying to sort out the issue and I think we're finally good to go with an acceptable implementation.

I won't drone on about the why's and wherefore's of the protracted investigation but suffice to say in summary that the large bespoke MEMC chip used within the Master to replace the Beeb's more classic arrangement of discrete IC's for address decoding and I/O control of sideways roms, doesn't produce (or at least doesn't allow access to) the correct signal regime to satisfy the requirements of the AT28C256 for reliable read and write operation. It's very close and only comes down to a matter of relative signal delays in in the order of tens of nanoseconds but to make an eeprom work in an internal sideways rom socket, it would require the addition of a further chip to gate-up some suitable controls. That being the case and although I did get a trial mod working, as far as I was concerned this was a game over because adding chips and complexity was simply not in the spirit of the thread's 'Holy Grail' theme.

What gives then...?

I had along the way tried hi-jacking some of the cartridge signals for internal use (differently decoded MEMC outputs) but once again, to no avail. Also, based on tests with my existing EELOAD and EEPnn software, eeproms didn't appear to work in a cartridge configuration but once I'd abandoned the internal eeprom configuration, I looked a little more closely at the cartridge side of things and discovered that actually, the signal regime is in fact suitable for (at least) a 28C256 but that there are a couple of significant arising quirks of operation of the eeprom that were stopping my software configuration tools from functioning. Cue version 4 of the software utilities as demonstrated in the video and we're almost there! (The eagle-eyed amongst you will have spotted one rom type-detect failure in the video but that's now sorted!)

The condensed upshot of all of this is that there are three options for using AT28C256 eeproms with a Master. These options are all cartridge-based and range from do-nothing plug'n'play with the V4 utils giving basic functionality to a simple cartridge mod giving the full works as available on a Beeb.

More tomorrow.... :D

EEPROM fitting in Model B and Master (small).png
(31.32 KiB) Not downloaded yet
Last edited by MartinB on Thu Aug 18, 2016 7:18 am, edited 1 time in total.

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby 1024MAK » Wed Aug 17, 2016 11:09 pm

And there he goes, leaving us hanging..... Again!

I look forward to the next instalment :D

Mark

PS I'm glad you mastered the problems with some of your Masters :P
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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby MartinB » Thu Aug 18, 2016 7:27 am

Mark wrote:And there he goes, leaving us hanging..... Again!

Heh heh, I'm not trying to be dramatic - I'm still away on holiday so forming a coherent story is more difficult without the actual gear in front of me!

Later.... :wink:

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby MartinB » Thu Aug 18, 2016 9:59 pm

A bit more... :wink:

I mentioned that there was a device type-detect error in the video (although now sorted) and this has been symptomatic of dealing with the slightly odd behaviour of an AT28C256 in a Master cartridge. Detecting the type of target chip is important in device programming utilities and is something that the V3 utils do, partly for user information and partly for ensuring that the tools behave sensibly. Ram is easy to determine because it writes in a single access with no significant delay and rom is also easy because conversely, it fails to write in a single access also with no significant delay. It is also worth noting that if ram is write protected, there is no way of differentiating this from rom but to the user, the functional implications are the same in that writing will not be possible.

When we come to eeprom, things get a little bit trickier and detecting viable eeprom versus locked eeprom versus ram and rom needs a little more care. An eeprom write cycle takes a finite time to complete, specified up to 10ms in the case of our subject device and it possible to use a fairly dumb programming algorithm using simple waits but this can potentially mean that programming might take minutes and detection of device types and errors becomes a little fraught. The chip designers have this covered though and the AT28C256 and similar devices have two mechanisms built-in to allow intelligent and efficient programming. The highest integrity of these is a function called Data Toggling where, during the post-write delay period, the eeprom toggles a single data bit on successive post-write reads (host polls) until the write is complete. It is this mechanism that my V3 and earlier utilities are predicated on and as you will probably know, it enables very fast and reliable programming with a 16k bank taking under 5 seconds.

Now comes the strange eeprom_in_a_Master_cartridge effect! Whilst we can write to the eeprom and the latter does correctly enter the post-write delay period ultimately successfully writing the data byte(s), Data Toggling simply doesn't work on post-write polling reads! :? #-o The device does respond to the reads in every other way but simply refuses to toggle the dedicated signalling bit. Again, long story short and without churning out pages of my test data and speculative discussion, let's just say that I ultimately put it down to a further vaguary of the MEMC signal set, took it on the chin and moved on!

(If anyone else has encountered this already and has any theories then feel free to contribute but it's not a show-stopper because I've already come up with a different way of programming and configuring the device.)

Straight away then, a different method of intelligent programming and type-detection was needed and fortunately, the AT28C256 provides a second method of reporting the in_write period and this is achieved by its statically inverting the top bit of the write data on post-write reads. Whilst this bit-inversion function is of lower integrity and more difficult to use in device type-detection, I have been able to suitably adapt the V4 utilities and maintain a fast-programming time with full error detection and this new functionality is seen working in the video.

Ok, nearly there! I can't make the V4 software available until I get home but I can cover the cartridge configuration options (with pictures!) and I'll do that in the next post. Maybe later or possibly tomorrow.... :wink:

(Hang in there Mark :lol: )

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby MartinB » Fri Aug 19, 2016 8:51 am

Before I continue with the cartridge details, I need to note one caveat that I haven't addressed yet - I think it's an easy one but I can't actually confirm that until I'm back home. Using the new V4 utils with an eeprom in a Master cart, I can configure, program and read the device to my heart's content including being able to freely read the programmed device from within BASIC or assembler. However, if I program the device with a standard sideways rom image and press <Break>, <Ctrl><Break> or switch-on or whatever, during the initialisation the rom doesn't get registered in the OS as a valid service or language rom.

On the Beeb, you will probably recall that even though an eeprom is difficult to corrupt and indeed can even be software write-locked, we still had to go on to fit a write-protect switch because of the machine hanging during a power-on or <Break> reset. This is due to the eeprom receiving a spurious or phantom write during reset which although it doesn't corrupt the eeprom, causes the device to enter the transient post-write offline state and it is this that appears to upset the Beeb start-up sequence and often results in a crash.

Very early on in the Master investigation, I had noticed that this installed effect doesn't seem to occur with the eeprom in a cart so I ignored it and happily pressed on with the rest of the work. However, it wasn't until I finished solving the other cartridge aspects and the software was suitably modified to the new V4 that I noticed roms weren't registering on a reset-start. So, I am assuming (with reasonable confidence) that on a Master too, we actually have exactly the same reset issue as on a Beeb but without the crash. I do know that during the *ROMS command a test write is deliberately carried out to each bank id to allow the writeable status to be displayed but I don't know if this happens routinely during Master post-reset initialisation? (This isn't the case on a Beeb because the *ROMS command isn't an inherent OS command, it exists in certain FS and other utility roms.)

In conclusion then, it appears a start-up write to each rom bank (intentional or otherwise), including the 0-3 cartridge-based id's, is sending our eeprom offline for a few milliseconds and although, unlike the Beeb, a Master doesn't crash in response, it does fail to register any eeprom-based rom images. The simple (well, fairly simple) solution then is exactly as per the Beeb implementation and we need to fit a hardware write-protect switch to our cartridge eeprom device. I stress that I haven't tried this yet but I'm confident it will sort the registration issue with the only down-side that there isn't actually a 100% do-nothing option as I suggested earlier and a further addition is needed to the cartridge details.

(Edits to fix a few slepping erorss...)
Last edited by MartinB on Fri Aug 19, 2016 5:01 pm, edited 4 times in total.

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby sydney » Fri Aug 19, 2016 1:40 pm

Martin do you know if this will also work with the new ara cartridge from retro hardware? I'm happy to test it for you if you don't know.
Cheers Simon.

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby MartinB » Fri Aug 19, 2016 4:55 pm

Remind me Simon - which is the ara? I have been talking to Dave H about these things in relation to MGC (although not just recently) but not the ara. Is this a cartridge manifestation that works in a Master and will take an AT28C256?

I used to have your email but I can't find it now - if you still have one for me can you ping me a hello and I can certainly send you a beta to try.... 8)

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby MartinB » Fri Aug 19, 2016 10:44 pm

So, let's assume the V4 utilities are a done deal and as per the previous package consist of EEP16, EEP32 and EELOAD. These represent an update from V3 for everyone because in addition to correcting (I guess adding) Master support, they are backwards compatible maintaining support for the Beeb and Elk and retain ADFS (spit) high-PAGE compatibility.

As discussed, there is a minimum mod that needs to be done to your cartridge and that entails adding a physical (hardware) write protect switch for the eeprom(s). I don't have a photo of a write protect modified Master cartridge because I had only just recognised the need prior to my going away but essentially, Pin 27 of the eeprom (could be two eeproms, see later) needs to be isolated from RnW by breaking the connection to cart IC3 Pin 12 (74HCT139). A DPST switch is then added to allow eeprom Pin 27 to be connected to either RnW from IC3 Pin 12 (Write Enabled) or to +5v (Write Protected). See the schematic further down where the Write Protect switch mod is shown in Red+Yellow.

If this one mod is carried out (first track cut alert!), nothing further needs to be done but note that an AT28C256 plugged into either or both of the cartridge sockets will (a) only yield 16k of it's 32k capacity and (b) cannot use the EEP16 facilities such as LOCK and ERASE. However, the device is (devices are) perfectly useable and can still be programmed and re-programmed quite happily using EELOAD.

Now, to at least enable use of the EEP16 functions, the previously described 'trick' of isolating Pin 1 (A14) and connecting it to Pin 2 (A12) is required - see earlier in this thread for a discussion of eeprom 'magic' addresses as depicted in the pictorial repeated below...

EEPROM Magic Addresses.png

Implementing the above 'trick' together with the Write Protect switch allows the use of one or two AT28C256 chips in the cartridge, each yielding 16k and offering EEP16 special functions.

The gold-plated solution however is to use one AT28C256 only in the cart IC2 position with a single 'leg lift' and to carry out one additional mod to the cartridge to allow A14 (effectively the upper/lower 16k selector for a 32k device) to be driven by the Master cartridge 0/1 or 2/3 rom id select signal. This simple mod (second track cut alert!) allows a single AT28C256 to yield its full 32k capacity as 2 x 16k roms and offers full functionality of the EEP32 configuration tools. The mod is depicted in the schematic below and there are a couple of accompanying photos.

Notes :
(1) In the schematic, the Write Protect mod is shown in Red+Yellow and the 32k mod in Red only.
(2) The photos do not show the Write Protect switch mod.
(3) The cartridge shown is obviously not a cream-coloured Acorn unit but is electrically identical as are all types normally encountered.

AT28C256 Master cart mods.jpg

Master AT28C256 32k (1).jpg

Master AT28C256 32k (2).jpg

Master AT28C256 32k (3).jpg


Questions....? :wink:

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby MartinB » Mon Aug 22, 2016 6:04 am

Back home so...

I've fitted a Write-Protect switch to the cartridge and confirmed that this done, everything works as expected. Here's a quick Shaky-Cam® demonstration. Note how said write-protect switch can be used to make eeprom rom images disappear and re-appear! :D

I'll push the V4 utils out in due course.



(Incidentally, 'normal' flash video embedding is working again! :shock: :? :D )


write protect.jpg

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby 1024MAK » Mon Aug 22, 2016 7:10 am

Words. Short. Early morning...

* Like * 8)

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

Postby boba » Mon Aug 22, 2016 1:14 pm

Very timely seeing as I've just restarted working on (I really mean 'playing with') :wink: my Master again. Oddly enough I've a Care cartridge just like your piccie so I'll just follow the idiot's guide. Just the v4 utils to come now (hint :wink: ).

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby MartinB » Mon Aug 22, 2016 1:39 pm

No worries, the V4 utils will indeed be out shortly! Since you have the same one, I'll post another couple of pics tonight of the cartridge PCB (the reverse side) to show the track-cut and pick-up points for the switch... 8)

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby 1024MAK » Mon Aug 22, 2016 3:26 pm

Martin, you may want to see if you can get a better picture of the first track cut (on the top side I think), otherwise it may be missed by the unwary.

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby MartinB » Mon Aug 22, 2016 3:53 pm

Will do... 8)

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby boba » Mon Aug 22, 2016 4:27 pm

MartinB wrote:No worries, the V4 utils will indeed be out shortly! Since you have the same one, I'll post another couple of pics tonight of the cartridge PCB (the reverse side) to show the track-cut and pick-up points for the switch... 8)


Every bit of help welcome for an ageing brain.

(Just realised how ageing after spending an hour or so debugging an *SRLOAD problem which turned out to be mistaking the numbering of the cartridge slots :oops: ).

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby MartinB » Mon Aug 22, 2016 9:42 pm

Some more pics....

The red wires as seen in the original pic and in two of the pics below are the single 32k eeprom mod and the grey 3-way wire length (a ribbon cable strip) is for the write protect mod. Any questions, just ask... 8)

Master eeprom cart 32k mod.jpg

Master eeprom cart WP mod 1.jpg

Master eeprom cart WP mod 2.jpg
(In the above pic, the grey wire to the switch centre is soldered in to a plated-through hole.)

Master eeprom cart WP mod 3.jpg

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby boba » Tue Aug 23, 2016 8:03 am

<pedant>
It's a SPDT switch, not DPST.
</pedant>

Ahhhhhhh! I feel so much better :wink: .

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Re: EEPROM - the Holy Grail of Sideways Rom?

Postby richardtoohey » Tue Aug 23, 2016 8:29 am

boba wrote:pedant
From what I've seen, Martin LOVES those. I'll get popcorn and a drink and you get the asbestos suit on. :shock:


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