dimented24x7

iTrader: (2)

Topic says it all. Id like to use one of the 28 pin eeproms in place of the crappy 2732 for tuning and then sparingly use the 2732's just for the final bins. I was looking at the pinouts for each and they look similar but it seems like there would be more to it then jsut hooking pin xyz to pin xyz. I dont really care about putting multple bins on one chip and having to offset the bin in the memory, i just want it to work.

Ken73

Simple. Put a 28-pin ZIF socket on the board, use a 28C64. Connect VCC from pin 26 to pin 28, and I think it's A12 to ground - then just program 000-FFF range with your BIN. That's what I've done for now, until I get the PROMinator working.

The nice thing is, it'll still work with a 2732A once you decide to put a permanent EPROM in it's place.

dimented24x7

iTrader: (2)

cool... so it really is just hooking up the address pins and what not for one chip to the other and grounding the remaining one to get the first 4k of the chip. Thanks ken...

Ken73

Yup! It's really that simple. I run that right now.. 28C64 - no eraser needed.

BIG 'G'

Sounds to simple but the electronicly challanged need more details, when you say put a 28 pin zif on the board, do you mean solder it on the board in place of the factory 24pin recepticle? Or is their an adapter that plugs into the factory adapter. Also it would appear that pin 26 is also conected to VCC along with pin 28 when the two are connected, and I'm only guessing but since pin1 and pin27 are left open your're only accessing 1/2 of the memory and the bin must be offset in the chip??

dimented24x7

iTrader: (2)

the factory 24 pin thing will have to go. I beleive thats the reason that C.M. stopped offering the adapter. I desoldered that thing and put a 24 pin ziff in its place. The stock socket for the prom is a real pita to remove so if you do decide to desolder it, be careful. I removed the plastic socket and just left the pins behind so i could desolder each seperatly. There are traces on both sides of the board meaning that the socket is soldered on both sides. If you jsut remove the solder and then take it off, you can pull the traces off. I also made a remote adapter on a project board and put a jumper on it so i can place a signal across the last adress pin if i ever need to have two bins on the chip and access them both. The socket on the adapter will be a 28 pin ziff so one (or more) of the address pins will be unused. All the other pins that the stock prom uses will be hooked up to the respective pins on the larger eeprom. The only reservations i have about the adapter is taht i might (or probably will) have interfierence problems causing the signals to and from the ecm to prom to be degraded. Ill see how it works though. As for the addressing. Theres no need to offset it if you just ground the unused pins. youll only be using the first portion of the chip. Theoretically what i did will work but ill wait untill its in the car and working to comment further. Heres a good link to how the addressing works. It helped me alot.



link

and a pic...

dimented24x7

iTrader: (2)

heres a pic of the pinouts of the chip mentioned above and the 2732...

Ken73

This is the same thing I did - just get a small flat-blade screwdriver and gently pry up on the stock socket. The plastic portion will come right off, leaving the individual pins.

Just so the unfamiliar people understand this - pulling traces off the board is BAD. (It ruins the board, and subsequently your ECM!) Take a soldering iron on one side, and use pliers or hemostats to pull the pins out from the other side. To get the hole clean, you can use desoldering wick (braided copper) and/or a "desoldering iron" .. Radio Shack sells one for under $20, I believe. It's a funky looking soldering iron that has a squeeze-bulb up by the handle that's connected to a hollow soldering head. Squeeze the bulb, hold the tip on the item you're trying to desolder, let the solder melt and let go - wa-la! Solder gets sucked into the desoldering iron.

This has been done in the past with very little success - with the bare ribbon cable. Adding a layer or two of aluminum foil wrapped around it has helped substantially from what I remember.

dimented24x7

iTrader: (2)

thats what i figured as well. The inside of the car is probably one fo the most em polluted places but what the hell, its worth a shot.

dimented24x7

iTrader: (2)

the other way i plan to do it if this one fails, which it probably will, and the way ken probably did it is to get a 28 pin dip socket and solder a jumper wire from pin 14 to pin 2 and solder a wire from pin 26 on the dip socket to pin 28 and put a ziff the socket for the eeprom and place the socket in the dip socket you soldered in the ecm with the pins 3-14 and 15-26 in the socket.

dimented24x7

iTrader: (2)

these 28C64 chips are sweet... they program in like a second and work in the ecm on the first shot.

Craig Moates

The 29C256 and 27SF512 chips will work just the same, even better since they're Flash. Pinout is the same, just ground or tie to Vcc the upper address lines.

BTW, I'm going to again offer an adapter which is a solder-in version of the old offering. You're right that the crappy GM socket is what the problem was. It will, however, require desoldering of the crappy socket.

TORC

So if I understand this right, the picture below would work as the layout for a simple adapter to use the 27C128 or 29C256 chip instead of a 2732A. With this setup, I'm assuming it used the 1st 32K of the chip's memory. How would this layout be modified to use the 2nd (or 3rd, etc.) 32K of the chip's memory

Craig Moates

Looks right. You might want to pullup the high address lines though just to be sure....

Then you just pulldown at each of the 'high' address lines to do the switching. I have some info over at www.moates.net

TORC

Ok, speaking specifically about the 29C256 chip, let me see if I have this straight. This would be a the layout for pulling up the 3 high address lines A12, A13 and A14 which would access the range 7000-7FFF:


and this would be the layout for pulling down the 3 high address lines which would access the range 0000-0FFF:


And different combinations of the address lines pulled up or down would access the remaining ranges. Is this right or do I have the pull up pull down thing backwards? Or am I not even close.... Thanks for the help.

TORC

Well, here's the results of my efforts... hand-drawn traces, hand-drilled misaligned mounting holes and self-etched but so far it check outs fine. I'll know for sure in a couple days when my 29C256's and ZIF socket arrive from Craig M. It's not the prettiest thing, but it seems to work so far...

MrBill

Your problem with that setup is not so much EMI from inside the ECM (or outside for that matter) as it is crosstalk. Think of it as EMI between adjacent wires of the ribbon cable. Even at only 1MHz (which seems to sound familiar for a 7747, as an example) the crosstalk in those ribbon cables is terrible.

Bill

dimented24x7

iTrader: (2)

i never did try it. I just constructed something similar to what torc did.