64K to 128K upgrade

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banedon88
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64K to 128K upgrade

Post by banedon88 » Fri Apr 24, 2015 12:41 am

Hi guys

I posted recelty in this thread (started by flaxcottage) with regard to upgrading my B+ from 64K to 128K by following this guide.
I've successfully done so and can see "Acorn OS 128K" as opposed to "Acorn OS 64K" that it had before.

What's puzzling is that the math doesn't quite add up.
Here's what the system should now have:

32KB of main RAM
32KB of I/O space and ROM (which we'll ignore as we're tlking about RAM)

Total: 32KB

In addition:

1x 32KB of RAM split into 20KB of shadow RAM and 12KB of sideways RAM

Running total: 32KB + 32KB = 64KB
This is the standard complement of RAM that a B+ 64K has.


Now, using the guide linked above we've added in 3x 32KB RAM chips and made the changes specified. This should give us 3x32KB = 96KB RAM.

64KB + 96KB = 160KB. Not 128KB.

I ran the sideways RAM checker program over my system (just in case the 128K banner is fixed to 64K,96K and 128K, but the RAM is still all there) and got this:
SWRAM _list.JPG
So... we have three sets of two sideways RAM, when we should have three sets of two plus one: three sets for the new 32KB chips and one single bank for the 12KB sideways RAM which is built in. Also, the total should still include both main RAM and sideways RAM as it does without the RAM upgrade.

So... why is the B+ not seeing the right number of banks? Is it hard coded not to?

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Elminster
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Re: 64K to 128K upgrade

Post by Elminster » Fri Apr 24, 2015 12:57 am

No that is correct. B+ doesnt have sideways ram by default and you have just add 3x2 of sideways RAM.

Have a read of this article instead.

http://martin-jones.com/2015/01/18/side ... o-model-b/

Explains it a bit better.

You see that there are 6x2 physical ROM slots and that 0/1 & C/D are missing. It is these that are created by the official Acorn daughter board.

What you have done is turned one of those Physical ROM slots into Sideways RAM and then added in the missing 2 socks (4 slots). That is a total of 3 chip and 96k or sideways Ram. 6 in total. All the rest are still physical ROMS slots.

So the diagram is output is correct and exactly what I have.

Why do you think you should have more? There are no more slots on the board physical or virtual. You only get 16.

EDIT: Corrected sideways/shadow madness
Last edited by Elminster on Fri Apr 24, 2015 8:00 am, edited 1 time in total.

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Re: 64K to 128K upgrade

Post by Elminster » Fri Apr 24, 2015 1:00 am

Also bear in mind Acorn only designed it to take 64k of shadow ROM. B+ is not supposed to have one of its physical sockets also turned into Sideways ROM. Acorn probably just never program he MOS banner to take that into account.

The changing banner is just a feature of the B+ , dont think off the top of my head if you up the Sideways RAM on a B or a Master it changes the banner.

So I would say it has been hardcode not to see it, it just has never been code to see it.
Last edited by Elminster on Fri Apr 24, 2015 8:00 am, edited 1 time in total.

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Re: 64K to 128K upgrade

Post by sydney » Fri Apr 24, 2015 7:32 am

I think there is some confusion over the terms shadow ram and sideways ram. The B+ does have shadow ram as standard. I think shadow ram shares address space with main ram from &3000 to &7FFF, sideways ram shares address space with rom from &8000 to &BFFF. This is my understanding of it, feel free to point out why I'm wrong. :D

The B+ has 32k main ram + 20k shadow ram + 12k sideways ram (64k), the addition of 3 * 32k (96k) sideways ram should give 160k. I have no idea why it does not display it correctly.

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Re: 64K to 128K upgrade

Post by Elminster » Fri Apr 24, 2015 7:59 am

Yes sorry names of sideways and shadow mixed up (it was 1am at the time). If they didnt both begin with S I might not mix them up all the time.

But B+ still not designed to have that mucd so I expect the person that wrote the MOS code didn't cater for it.

I wonder if the B+ MOS is deassembled anywhere to go have a look.

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Re: 64K to 128K upgrade

Post by banedon88 » Fri Apr 24, 2015 8:21 am

I think that the DFS 2.26 replaces the banner that the MOS puts out. So you do end up with 'Acorn OS 64K', but then I think it over writes it with 'Acorn OS xxxK'
(where xxx is the amount of RAM).
So we'd have to disassemble the DFS ROM. I think I might take a look when I'm very bored :mrgreen:.

In the meantime, I could just remove the SWRAM expansion and then re-run the SWRAM detection code to see if it picks up the inbuilt 12K bank at that point.

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Re: 64K to 128K upgrade

Post by TheCorfiot » Fri Apr 24, 2015 8:22 am

Believe it or not it's the 1770DFS Rom that overwrites the MOS's original 64K startup banner to display 128K if the additional SWR or daughterboard is detected.

If you have the older version of 1770DFS in the B+ then 64K is always displayed by the MOS regardless of the daughterboard being present or not as the DFS does not overwrite the startup banner.

It's a static programmed banner too, ie not calculated to reflect actual RAM, just one of the 2 Factory options.

To prove this pull out your DFS ROM and see your startup banner revert to 64K

Hope that clears things up.

:)

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Re: 64K to 128K upgrade

Post by Elminster » Fri Apr 24, 2015 9:21 am

The bit about not being calculated cant be right.

I have seen it say 80k, 96k, 112k as well as 64 & 128k as well.

I had problems with seating of my SRAM and it kept changing.

In the link above, repeated below, you can also see it says 96k

http://martin-jones.com/2015/01/18/side ... o-model-b/

Perhaps DFS 2.26 of ADFS 1.3 has slightly different code in it?

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Re: 64K to 128K upgrade

Post by 1024MAK » Fri Apr 24, 2015 9:31 am

Maybe this helps a little:-
Acorn introduced the Model B+ in mid-1985, increasing the total RAM to 64 kB and including floppy-disk support as standard, but this had modest market effect. The extra RAM in the Model B+ BBC Micro was assigned as two blocks, a block of 20 kB dedicated solely for screen display (so-called "Shadow" RAM) and a block of 12 kB of 'special' Sideways RAM. The B+128 came with an additional 64 kB (4 × 16 kB "Sideways" RAM banks) to give a total RAM of 128 kB.
Shadow RAM is where the display data is located when operating in the extra screen modes so as to free up main RAM for larger programs.

I don't know enough about the B+, but in the later Master 128, some of the "extra" RAM is mapped to part of the OS ROM address range, not the sideways ROM area.

Mark

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Re: 64K to 128K upgrade

Post by banedon88 » Fri Apr 24, 2015 5:24 pm

Ok, looking at a raw dump of the DFS 2.26 ROM file I can see that it lists "Acorn OS ",a null charcater, "K", then followed by various select values separated by null: 64, 89, 96, 112, 128. 144, 160

Here's a picy:
DFS2.26-rom-capture.PNG
So, it looks like it doesn't manufacture then number, but possibly uses a lookup table instead. I'll take a look at the code a bit later when I get a chamce to pick disassemble and pict it apart.

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Elminster
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Re: 64K to 128K upgrade

Post by Elminster » Fri Apr 24, 2015 6:12 pm

banedon88 wrote:Ok, looking at a raw dump of the DFS 2.26 ROM file I can see that it lists "Acorn OS ",a null charcater, "K", then followed by various select values separated by null: 64, 89, 96, 112, 128. 144, 160
Interesting

So, it looks like it doesn't manufacture then number, but possibly uses a lookup table instead. I'll take a look at the code a bit later when I get a chamce to pick disassemble and pict it apart.

That fits in with what I put above that I saw 64, 80, 96, 112, 128. (Think you meant 80 not 89(

Before I soldered my SRAM into aturned pin socket it kept popping out of the board giving different values. Not seen 144 or 160 tthey might not be related as all the ohter number go up in 12's. (128+12 = 140 and 144+12 =156).

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Re: 64K to 128K upgrade

Post by jgharston » Fri Apr 24, 2015 7:38 pm

banedon88 wrote:So we'd have to disassemble the DFS ROM. I think I might take a look when I'm very bored :mrgreen:.
already done.
You might be able to see that the code only checks for SRAM in banks 15-12 and 1-0. Any SRAM in other banks are not counted, which is why you get the wrong banner on your machine, your RAM in banks 6 and 7 are not counted. For a full RAM count you want RAMCount.
Elminster wrote:I wonder if the B+ MOS is deassembled anywhere to go have a look.
mdfs.net/System/ROMs/AcornMOS/BBC_200/

Code: Select all

$ bbcbasic
PDP11 BBC BASIC IV Version 0.32
(C) Copyright J.G.Harston 1989,2005-2020
>_


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Re: 64K to 128K upgrade

Post by banedon88 » Fri Apr 24, 2015 8:39 pm

jgharston wrote:
banedon88 wrote:So we'd have to disassemble the DFS ROM. I think I might take a look when I'm very bored :mrgreen:.
already done.
You might be able to see that the code only checks for SRAM in banks 15-12 and 1-0. Any SRAM in other banks are not counted, which is why you get the wrong banner on your machine, your RAM in banks 6 and 7 are not counted. For a full RAM count you want RAMCount.
Elminster wrote:I wonder if the B+ MOS is deassembled anywhere to go have a look.
mdfs.net/System/ROMs/AcornMOS/BBC_200/
Excellent - nice find :).

There's a little space at the end of the ROM so I'm tempted to make a version which checks all 16 banks... :)

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Re: 64K to 128K upgrade

Post by jgharston » Sat Apr 25, 2015 11:13 am

banedon88 wrote:There's a little space at the end of the ROM so I'm tempted to make a version which checks all 16 banks... :)
All you'd need to do is change the CPX at &BFEF:

Code: Select all

BFEC CA          Ê    DEX		Decrement ROM number
BFED 30 08       0.   BMI &BFF7		All done, jump to return
BFEF E0 0B       à.   CPX #&0B		Loop for ROMs 15-12
BFF1 D0 E0       Ðà   BNE &BFD3		Skip ROMs 11-2
to:

Code: Select all

BFEC CA          Ê    DEX		Decrement ROM number
BFED 30 08       0.   BMI &BFF7		All done, jump to return
BFEF 10 E2       à.   BPL &BFD3		Loop for all ROMs
BFF1 D0 E0       Ðà   BNE &BFD3		Never executed

Code: Select all

$ bbcbasic
PDP11 BBC BASIC IV Version 0.32
(C) Copyright J.G.Harston 1989,2005-2020
>_

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Re: 64K to 128K upgrade

Post by banedon88 » Sat Apr 25, 2015 12:40 pm

The only other change might be to change the byte being tested to something further "down", as the inbuilt sideways RAM in the B+ is only 12K and so extends from &8000 to &AFFF, where-as the DFS code tests &BFFF.

BTW the DFS 2.26 ROM image that I've got does not correspond with the disassembled one in the above link. I suspect the code is the same - just not in the same place in the ROM.
Just to be sure, I read my DFS 2.26 ROM (which I use in my B+) into my EEPROM programmer and it's the same as the image.
So the one in the link is probably from a different version of the ROM or from an ADFS ROM.

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Re: 64K to 128K upgrade

Post by jgharston » Sat Apr 25, 2015 7:25 pm

banedon88 wrote:The only other change might be to change the byte being tested to something further "down", as the inbuilt sideways RAM in the B+ is only 12K and so extends from &8000 to &AFFF, where-as the DFS code tests &BFFF.
Very bad. The byte tested should (or in RFC parlance. [MUST) be &8008, as that is the binary version number and is not used for anything else. If the machine crashes between modifying it and restoring it it will have no effect other than the binary version number changing. If any other byte is changed, it changes the functionality of the code.
banedon88 wrote:BTW the DFS 2.26 ROM image that I've got does not correspond with the disassembled one in the above link. I suspect the code is the same - just not in the same place in the ROM.
So the one in the link is probably from a different version of the ROM or from an ADFS ROM.
It's not from the ADFS ROM, it's from the DFS ROM. I thought I had disassembled the DFS ROM that comes with B-Em, and just checking it's DFS 2.26. I wonder if I disassembled the ROM from my actual B Plus, and checking, that's DFS 2.10.

Code: Select all

$ bbcbasic
PDP11 BBC BASIC IV Version 0.32
(C) Copyright J.G.Harston 1989,2005-2020
>_

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Re: 64K to 128K upgrade

Post by DutchAcorn » Sun Apr 16, 2017 8:17 pm

I also did this upgrade, following the same guide. With sites disappearing it seems practical to repeat the described technique here:
http://www.firths.org/bbc/my_b+128k.html wrote:
  • Stack up 3 43256, 62256 or equivalent devices (e.g. Farnell part number 209-7992 or 209-7986)
    Fold pins 1 (A14) and 27 (WE) up on all three devices.
    Fold pin 20 on the top device up, and on the middle device out horizontally.
    Solder all pins on all devices together (except the pin 20s)
    Attach an 'ezihook' (or equivalent) to the pin 1 group, the pin 27 group, and the two extra pin 20s.
You now have a three high ROM module, with 4 'ezihooks' attached.

To use it:
  • Place the module into a spare ROM socket
    Connect the pin 1 ezihook to a source of the LSB of the ROM select bus (The east-most pin of link L9, L11, L12, L15 or L18 is the obvious choice)
    Connect the pin 27 ezihook to a source of a write strobe (e.g. pin 24 of the 7002)
    Connect one of the extra pin 20s to pin 9 of IC46 (the chip select for ROMs 12 and 13)
    Connect the other extra pin 20 to the spare pin of L13 (CS for either roms 0/1 or 14/15, depending on where you want BASIC)
It does not matter which of the pin 20 ezihooks you connect to which location - this would just swap which of the two piggybacked RAM chips was in which banks.
If your RAM is installed correctly it should detect RAM in banks 0,1,12,13 and two other banks, depending on which socket you installed the module in.
The result in my B+ (I like my wires concealed :D):
128K upgrade.jpg
What bugs me though is the fact that the SWRAM check supplied on the disk with the 64K basic for the B+ 128K (attached) fails on my B+. The test program is called "TEST" and runs after pressing break. It also fails in BeebEm, perhaps there's more to the B+128 than just a few extra RAM banks? #-o

Or did I find the wrong B+ 128K support disk image?

Any thoughts?
Attachments
B+128K.zip
(17.34 KiB) Downloaded 42 times
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Re: 64K to 128K upgrade

Post by flaxcottage » Sun Apr 16, 2017 8:37 pm

The big test on this is can you successfully load 6 sideways ROMs into the new RAM. If you can and the images work then it does not matter what the test shows - the conversion works. :D

My conversion works perfectly. I've added a turboMMC system and from Shift-Break I can load various combinations of ROMs without problem.
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Re: 64K to 128K upgrade

Post by DutchAcorn » Sun Apr 16, 2017 8:58 pm

flaxcottage wrote:The big test on this is can you successfully load 6 sideways ROMs into the new RAM. If you can and the images work then it does not matter what the test shows - the conversion works. :D

My conversion works perfectly. I've added a turboMMC system and from Shift-Break I can load various combinations of ROMs without problem.
The sideways ram banks all work fine, but it seems strange that the test from the support disk fails. Did the real B+ 128K upgrade have something special or is the test program flawed... :?
Paul

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Re: 64K to 128K upgrade

Post by DutchAcorn » Thu Apr 20, 2017 9:55 pm

Another thought: on the B+ the OS and Basic are combined into one 32K ROM. If the OS needs to be accessed the OS signal is used as a rom select signal to access the OS.

This means that, if you have BASIC in slot 15 you can not use slot 14, even on a B+128K. Or, in other words, BASIC always occupies two ROM slots.

What if you would
  • burn a separate 16K EPROM for the OS and place that at IC71 (BASIC/OS socket)
    Remove S13 (which selects 15 or 1 as the default bank for BASIC)
    Short pins 1 and 2 on IC34 so that IC71 CS is controlled only by OS
    piggyback a 32K EPROM with BASIC + (other ROM) onto the new OS EPROM in IC71
    Isolate and make a flying lead for pin 27 on the piggybacked EPROM to pin 7 on IC46 (rom select for 14/15).
Would that enable you to use bank 14 for a ROM? Or would you need to isolate pin 27 of the new OS rom and lead that to 0V?

Or is this all a silly thought? :D
Paul

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Re: 64K to 128K upgrade

Post by DutchAcorn » Fri Apr 21, 2017 8:45 am

DutchAcorn wrote:Another thought: on the B+ the OS and Basic are combined into one 32K ROM. If the OS needs to be accessed the OS signal is used as a rom select signal to access the OS.

This means that, if you have BASIC in slot 15 you can not use slot 14, even on a B+128K. Or, in other words, BASIC always occupies two ROM slots.

What if you would
  • burn a separate 16K EPROM for the OS and place that at IC71 (BASIC/OS socket)
    Remove S13 (which selects 15 or 1 as the default bank for BASIC)
    Short pins 1 and 2 on IC34 so that IC71 CS is controlled only by OS
    piggyback a 32K EPROM with BASIC + (other ROM) onto the new OS EPROM in IC71
    Isolate and make a flying lead for pin 27 on the piggybacked EPROM to pin 7 on IC46 (rom select for 14/15).
Would that enable you to use bank 14 for a ROM? Or would you need to isolate pin 27 of the new OS rom and lead that to 0V?

Or is this all a silly thought? :D

Actually it is a lot simpler than I assumed:
  • Remove the jumper on S13 (which selects 15 or 1 as the default bank for BASIC)
    piggyback a 32K EPROM with BASIC + (other ROM) onto another ROM (not the OS ROM)
    Isolate and make a flying lead for pin 20 on the piggybacked EPROM to the south pin of S13 (rom select for 14/15).
To "prove the concept" I made a provisional implementation with a 32K ROM with DFS and BASIC:
piggy.jpg
screen roms.jpg
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Re: 64K to 128K upgrade

Post by DutchAcorn » Fri Apr 21, 2017 9:16 am

Or, using the same technique with a RAM chip in addition to the 128K configuration as described in the first post of this thread offers sideways RAM in the range that is counted by the DFS :D
160K.jpg
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Re: 64K to 128K upgrade

Post by rmbrowngr » Thu Mar 14, 2019 2:37 pm

Very interesting now I have a B+ 64k. So, what was final "best" instructions to do this upgrade?
Richard B
Acorn Electrons issue 4 and 6, MRB, Plus 1, AP6, AP5, Pegasus 400, BeebSCSI, Gotek, Raspberry Pi, GoSDC MBE.
BBC B+ 64K (128K upgraded) with Duel OS, Raspberry Pi and Gotek.

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Re: 64K to 128K upgrade

Post by Sniffer » Tue May 07, 2019 4:05 pm

Old thread I know but I'm just having a play with this, trying to get my head around it, so as to do the upgrade.
To "prove the concept" I made a provisional implementation with a 32K ROM with DFS and BASIC
I have also created a rom with DFS & BASIC, concatenated together in a 32K ROM. BASIC on top followed by DFS. I've piggy backed that ROM onto another ROM (containing ADT and FDC), isolating pin 20. Reomoved the jumper at S13 and attached a lead between pin 20 of the piggy backed ROM and S13(south).

What I get is the Language? prompt.

If I replace the jumper at S13, leaving everything else in place, I get;

Code: Select all

>*ROMS
Rom 15 : (S ) DFS 2.26
Rom 09 : (S ) ADT 1.3
Rom 01 : ( L) BASIC
So, am I missing something or are these results expected?

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Re: 64K to 128K upgrade

Post by Sniffer » Tue May 07, 2019 4:37 pm

Please ignore my post above, I hadn't set things up correctly. User error once again!

Edited to say, I do have a question though. Why fold all the #1 & #27 pins up if you are to solder them all together? Surely it's easier to just fold up the bottom device's pins?
Last edited by Sniffer on Tue May 07, 2019 5:21 pm, edited 1 time in total.

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Re: 64K to 128K upgrade

Post by DutchAcorn » Tue May 07, 2019 6:37 pm

Sniffer wrote:
Tue May 07, 2019 4:37 pm
Please ignore my post above, I hadn't set things up correctly. User error once again!

Edited to say, I do have a question though. Why fold all the #1 & #27 pins up if you are to solder them all together? Surely it's easier to just fold up the bottom device's pins?
Yes, it is. You only need to do the bottom ones for 1 and 27.
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Re: 64K to 128K upgrade

Post by Sniffer » Tue May 07, 2019 7:18 pm

Yes, it is. You only need to do the bottom ones for 1 and 27.
Ok, thanks fo that.

Another question. With the original upgrade, one of the pin 20s is taken to S13(south), which is fine. With your adaptation (over at viewtopic.php?f=3&t=16789, you suggest the newly added top device's pin 20 also goes there. So S13(south) has the two leads? That doesn't seem correct?

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Re: 64K to 128K upgrade

Post by DutchAcorn » Tue May 07, 2019 8:01 pm

Sniffer wrote:
Tue May 07, 2019 7:18 pm
Yes, it is. You only need to do the bottom ones for 1 and 27.
Ok, thanks fo that.

Another question. With the original upgrade, one of the pin 20s is taken to S13(south), which is fine. With your adaptation (over at viewtopic.php?f=3&t=16789, you suggest the newly added top device's pin 20 also goes there. So S13(south) has the two leads? That doesn't seem correct?
In the original upgrade, one of the pin 20s is taken to L13, not S13?
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Re: 64K to 128K upgrade

Post by Sniffer » Tue May 07, 2019 8:16 pm

In the original upgrade, one of the pin 20s is taken to L13, not S13?
My bad. I think I need to get this senility looked at :) I thought L13 meant S13, don't know why!
Last edited by Sniffer on Tue May 07, 2019 8:18 pm, edited 1 time in total.

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