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2001-8 Chicklet Pet Fault Finding.

giobbi said:
[[ Hi Mike! How are you? ]]


In this article you can find both RAM and ROM adapter especially made for PET 2001/8; also a Video RAM adapter, just in case you run out of RAM chips.

http://www.8bit-homecomputermuseum.at/repair/bluepet/bluepet.html
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I'm fine thanks, although it's a little warm here right now; how about you? You had some excitement down there...

Yeah, Nicolas makes/sells some pretty useful RAM & ROM goodies, although I understand they can be a little hard to get sometimes. D'Asaro's stuff is also useful, but the RAM & ROM adapters only replace one chip at a time. Lots of options...

Nice to touch base again!

M
 
MikeS said:
Here's one man's approach to replacing the RAM; kludgy's definitely the word, but hey, it works!
(You should see the ROMs ;-) )

It's a little more complicated than necessary because he provided a switch bank to permit different RAM sizes.

Note that it's installed underneath the board so that it looks normal on top.

I can probably find the schematic in case anyone's actually interested

View attachment 33035
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Hi Mike nice to see you back!

I can see why it's underneath the board, as you say kludgy but hey if it works not everything is beautiful!

Can you post the schematic I would be interested in seeing it!
 
Hi, and thanks for the kind words. It's good to be back, although I'm spending a little less time here these days; can't add much to Dave's most excellent diagnostics.

Can't find that schematic at a quick look through my files but the genius in question is local and a friend so I'll ask him to send me a copy if he still has it; might be a few days because he's off to VCF MW this weekend.

Not directly related to RAM issues, but here's one of Jim's 6540 adapters. As is, it's also just one at a time like D'Asaro's but the DIP switch (or jumper) lets you select which ROM image you want; the one shown contains BASIC 1 and 2/3; plug it into the appropriate 6540 socket, set the DIP switch for the version and location and Bob's your uncle.

ROMadapterB.JPG

With a few jumpers to the main board chip selects etc. you can effectively let the computer select the bank and replace all the ROM chips with one.

If you want to play with the EPROM contents you can kludge a R/W signal and use a battery-backed RAM chip instead of the EPROM; load it up with a starting image on your programmer and then plug it in to the PET, either in the end location or an unused block for editing.

Finally, with a few more kludgy jumpers you can use it to replace the RAM chips as well.

Then again, you could just order a PETVET! ;-)
 
That looks very ingenious, I like how minimal and compact that is as a solution!

I know what you mean about getting a PetVet, it may be the answer although I am taking advantage of this fault
to learn more about RAM etc..

Just a quick question is it dynamic Ram that has Row and Column and static uses address lines?
 
Pet Rescue said:
That looks very ingenious, I like how minimal and compact that is as a solution!

I know what you mean about getting a PetVet, it may be the answer although I am taking advantage of this fault
to learn more about RAM etc..

Just a quick question is it dynamic Ram that has Row and Column and static uses address lines?
Click to expand...

Well, both DRAMs and SRAMs have address lines and in fact most SRAMs also have rows and columns internally ;-)

SRAMs don't need refreshing and the individual chips are simply selected by enabling the appropriate chip select(s) and/or the R/W signal.

DRAMs on the other hand do need to be refreshed periodically, usually by sequentially accessing all the rows; a chip is selected by simultaneously enabling the appropriate RAS and CAS signal and of course the R/W signal as appropriate; this makes signal timing somewhat more complicated and critical than SRAMs.

I've never tried it but I suppose you could replace DRAM with SRAM by ignoring RAS and using a (possibly modified) CAS signal as a chip select.

At least that's how I understand it; corrections and criticism welcome.

m
 
MikeS said:
Well, both DRAMs and SRAMs have address lines and in fact most SRAMs also have rows and columns internally ;-)

SRAMs don't need refreshing and the individual chips are simply selected by enabling the appropriate chip select(s) and/or the R/W signal.

DRAMs on the other hand do need to be refreshed periodically, usually by sequentially accessing all the rows; a chip is selected by simultaneously enabling the appropriate RAS and CAS signal and of course the R/W signal as appropriate; this makes signal timing somewhat more complicated and critical than SRAMs.

I've never tried it but I suppose you could replace DRAM with SRAM by ignoring RAS and using a (possibly modified) CAS signal as a chip select.

At least that's how I understand it; corrections and criticism welcome.

m
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Thanks for the info Mike, I was wondering why dynamic RAM's have RAS and CAS I mistakenly thought they were Row and Column related.
I didn't see them on static RAM's so thought they just used the address lines only.
Do you know any good books where I could learn more about RAM chips etc?
 
Pet Rescue said:
Thanks for the info Mike, I was wondering why dynamic RAM's have RAS and CAS I mistakenly thought they were Row and Column related.
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They are indeed related (Row Address Select, Column Address Select).

Internally most RAM chips are arranged in a row/column matrix; in the case of SRAM this is transparent since an internal address decoder converts the external linear address to row/column coordinates and the Chip Select pin(s) enable(s) the inputs and outputs.

A dynamic RAM has two separate select pins and decoders, one for the rows and one for the columns; that lets you just step through all the rows (128 in the case of a 4116) to refresh the memory cells instead of having to refresh all 16,384 cells individually. To address an individual cell and enable I/O you select both RAS and CAS simultaneously.
Do you know any good books where I could learn more about RAM chips etc?
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Not off hand, but studying a few data sheets and some judicious Googling will probably find lots of useful material.
 
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Thanks Mike for answering my questions, I sometimes wonder if they appear daft questions as my knowledge is weak in some areas of electronics.
It helps gain more of an understanding and builds confidence!
 
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