Help reading TC5518 Static Ram from Tractor monitor

On 25 Mar 2006 09:06:03 -0800, "ve3tjd" put finger to keyboard and composed:

Is the uP socketed? If so, remove it. Then wire the address and data pins of your pocket programmer to the uP socket, and the CS pin to the CS of the SRAM (or to the uP socket, if applicable). Connect the OE* pin of the programmer to the R/W pin of the SRAM, through an inverter if necessary. Now read the data as you would for a 2716 EPROM.

When writing the data, you may be able to "program" the SRAM as you would a 2716 EPROM or a 2816 EEPROM - just don't connect the Vpp pin.

- Franc Zabkar

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I would have thought it /extremely/ unlikely that any manufacturer (especially of a unit to be used in the wild) would trust his program to RAM. Are you certain that there is no ROM (with the RAM being used as data storage)?

Geo

On Sun, 26 Mar 2006 16:55:06 GMT, Geo put finger to keyboard and composed:

25 years ago a colleague was involved in the design of a RAM based point-of-sale system. I considered it a reprehensible product at the time and I still do.

- Franc Zabkar

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Hi Franc:

Thanks for your input. First, I would like to reply to Geos reply. There is a 2764 right next to the SRAM, but I've tried to read the eprom and it contains no data. On the working unit I have, I took another 2764 (NOT THE ORIGINAL!!) and erased it (all FF's) and reinstalled it and it still worked normally, telling me the code isn't on the 2764.What is the purpose of the 2764....I don't know.

The uP isn't socketed, so grabbing the address and data lines from this angle won't work. I socketed the broken units uP as I thought that it was shot, so once I get the data OFF of the good unit, programming should be fine.

for the 2716. Do you think the uP address and data lines would cause too much of a load for the programmer to allow me to try and read it while the uP is in place?

Why am I so worried.... well, these boards are no longer made anymore and I don't want to kill the good one by trying to fix the bad one! No schematics are available (the board was made by TRW in England), so without reverse engineering the 4 layer board, I think we have to use common sense with the layout of the "system".

The easiest thing to do would be to solder leads onto the SRAM while it's in the board, and connect them to the programmer for reading.That's why I ask if you think it will hurt to leave the uP in place.

Thanks again guys,

Tedd, VE3TJD

On 30 Mar 2006 06:22:03 -0800, "ve3tjd" put finger to keyboard and composed:

If you remove the 2764, does the device still work?

Is it possible that the "dummy" 2764 could be a place holder for a diagnostic EPROM??? Could such a chip be used to initialise the SRAM with factory defaults??? Once the SRAM is initialised with functional code, could the EPROM be replaced with an "all-ones" dummy that would cause the uP to cycle through its addresses until it hits the RAM code???

I don't know, but you would need to ensure that the uP was in reset mode so that its address and data lines would be high-Z.

I'd experiment by reading and writing the RAM in the bad board.

- Franc Zabkar

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