527 RAM expansion board switches

[tezza]

Hi Guys,

I’m wondering if any OSI gurus out there might be able to help me with this problem?

I have a OSI 527 RAM expansion board I want to add to my cassette-based C4P.. . The board has some unconnected switches/jumpers on it. Apparently these can be used to specify exactly where you want to put the three 8k banks on the board in memory.

I don’t know how to jumper the board to do this? Does anyone know? I need the board to occupy a continuous 24k block of RAM starting at the end of the 8kRAM on the 502 board fitted, so I guess from 2000H onwards?

Some more info…

Here are the switch points (W1, W2 and W3) on my board which need bridging.



and here is the relevant part of the circuit diagram.



I found an article in "Micro: the 6502/6809 journal Vol 37 (June 1981)" which had a piece on adapting the OSI 527 board to a 600 Superboard. In that article was this statement:

"Jumpers W1, W2 and W3 at F9 determine the starting addresses of three independent 8k blocks of memory on 8k boundaries. No changes are made here...".

The 600 board has RAM (starts 0000H) and BASIC (starts A000H) which are at the same positions in memory as my 502 board so I figure that advice also applies to me.

What is the default though? On my board it looks like there were default tracks connecting these switches but they have been completely scraped away. However using the low-res B/W photo in the article I can just see where these default tracks should go.



I wired up the system so the tracks connected as shows. Booting up the C4P now shows a RAM capacity of over 18000 bytes, which is progress So I am getting SOME of the RAM on the 527 board. With a fully populated RAM board plus the 8k on the 502 I should be seeing something close to 32k though, yes?

I could be a faulty RAM chip BUT I could also have those switches wrong? I don't want to try an diagnose a faulty RAM chip if it's the settings that are the problem. Can anyone verify they are correct for my configuration?

Any comments welcome.

Tez

[tezza]

Update:

I do have the board configured correctly. Dave confirmed it via the classiccpm mailing list a couple of days ago but the letter ended up in my Gmail spam folder for some reason? I've only just seen it.

Obviously a crook RAM chip or socket somewhere.

[nama]

I have a couple of good ram test progs that I'll send your way.

Phil

[nama]

Just for completeness, and for those who may come looking at a later date, I have posted Dave's classiccpm comments:

W1->F9 pin 14 (Y1 = $2000)
W2->F9 pin 13 (Y2 = $4000)
W3->F9 pin 12 (Y3 = $6000)

which allows the 8K block at $0000. If you had a 505 board and one 527, you'd move W3 over to the Y0 output on pin 15 of F9 ($0000), and have a solid block from $0000-$5FFF.

Make sure, if you're adding the 527 into a system that previously only had a 502 and 540 board, that you add a second power supply for the 527 (which can be powered via the side power connector), or replace the original supply with a beefier supply, because the 527 will suck a lot of current and the single supply can't handle the additional load.

[tezza]

I have a couple of good ram test progs that I'll send your way.

Phil

Thanks Phil

Received.

[tezza]

Well this looks good...

It was a single faulty RAM chip. Not bad considering there are 48 on the board!



Incidentally I'm playing with this OSI gear as part of RetroChallenge month. Users of this board might like to see progress so here is the URL:
http://www.classic-computers.org.nz/blo ... -board.htm

Chances are I'm going to need more help

Tez

[dave]

Hi Terry,

Welcome! This is a small community, but you'll find there are some sharp folks here. And interestingly, an outsize contingent of talented Kiwis

Well this looks good...

It was a single faulty RAM chip. Not bad considering there are 48 on the board!

Incidentally I'm playing with this OSI gear as part of RetroChallenge month. Users of this board might like to see progress so here is the URL:
http://www.classic-computers.org.nz/blo ... -board.htm

Chances are I'm going to need more help

Tez

Awesome that you are doing an OSI retrochallenge, and nice web site! Good for you that you calculated the chips to check rather than just going down the line. That may seem obvious to a trained engineer, but it's not obvious to everybody, and despite your modesty in describing your skills on the website, it shows that you're employing an enlightened approach to hardware. Good luck on the retrochallenge!

Dave

[tezza]

Awesome that you are doing an OSI retrochallenge, and nice web site! Good for you that you calculated the chips to check rather than just going down the line. That may seem obvious to a trained engineer, but it's not obvious to everybody, and despite your modesty in describing your skills on the website, it shows that you're employing an enlightened approach to hardware. Good luck on the retrochallenge!

Dave

Thanks for those kind words Dave, and for your website which I've made extensive use of.

I'm updating the OSI retrochallenge project page almost daily. Members of the forum might find it interesting to check on progress (or lack of it). Just use the link above

Tez