You'll never guess what I've gone and done. This one's a bit more complicated than the 2-page one, and uses more bits. But it's still less complicated than the Mines way of doing it, (again) it's not based on what they done, and it doesn't need a daughter board.

 

For this, you basically solder a socket on top of a 27C512 and connect all pins together except pin-20, which you leave apart. Bend up pin-1 again. Basically, do the 2-page mod first... this gives you the hi/lo selection in the both EPROMs. The second switch is to select which EPROM will be used (top/bottom). Unfortunately, the EPROM that's not in use at the time needs it's pin-20 pulled high, while the in-use EPROM is connected to the ECU socket. It can be done with a 6-pin (double throw) switch. I'll stick a pic up and the details when I've yanked it out of my car again. Wiring to the second switch basically comes from the 2 pin-20s on the EPROMs (one on the top socket, one on the bottom EPROM), the pin-20 from the ECU socket, and the 5V pin (pin-28).

 

I tried it out earlier and it works just loverly. I'm running standard UK and SE in the bottom EPROM and the same again in the top, but with the rev limit set to 5K and the speed limited to 85mph (137kph). It actually topped out at around 90 on the speedo (it's great having access to a private track), and the rev limit kicked in (rather violently :) ) at pretty much 5K.

 

Alright?

Well done mate, I'll be after one of these myself when I get the car back on the road.

I'd given up messing with the codes as I couldn't really test them :(

Yeah, tell me about it Chris! I've started getting all interested in this stuff again because I'm finally a 300 driver again! I'll probably jinx it just by talking about it, but it's booked for Pete to be doing the mapping and injectors next week. It's gonna kick ass! When are you expecting yours back?

 

Anyway, the mod's a slice of pie to make (not quite a piece of cake, but almost). It's probably too late to be talking about it... I forgot to mention: programming is the same as the 2-page mod, except you've obviously got another switch to flick, and I also forgot to say pin-20 on the bottom EPROM should be bent out so it doesn't connect with the ECU (unless via the switch). And you need to pull the top EPROM out so you can erase the bottom one (obviously really).

 

And, you don't have to stuff a 27C512 in the top socket - if you've only got a 27C256 you can use that instead. Obviously, the 1st switch won't have any function if the 256 is selected.

 

And I /really/ forgot: the second switch most DEFINITELY shouldn't be switched while the car is running! There'll be a point where the switch isn't quite connected to anything, which means the ECU will think neither EPROM is connected. It'll basically miss a whole load of instructions it should be executing and could end up doing something horrible.

 

And I should probably also put some sort of disclaimer... you mess with your ECU, you run the risk of screwing it up. I'm not responsible. There, how's that?

Is there any reason why you can't use a 27C010, or 27C020, etc, rather than 2 27C512s?

Well, the Mines mod used a 27C1001 (1Mbit) but it needs a daughter board because it's got more pins. So it doesn't really fit in with the plan of grabbing a few cheap bits and slapping them together (which anyone can do, right?). I don't wanna be accused of ripping Mines off either (not a dig at you Chris) - not that it'd really be a problem, because it's an old design and I don't think they'd give a stuff. Besides, it's kinda convenient to be able to whip the top EPROM out, erase it / re-program it and still have one in the ECU in case you need the car.

It's a different way of doing it. Maybe not the best, but convenient.

After kind of stealing Si's idea, and talking to him about it, I'm going to make a daughter board to take a 27C1001 and run 4 maps.

Shouldn't be too hard to do in theory.

:) You didn't steal it John - you suggested 4 maps, so I thought I'd better come up with a way to do it with the bits I've got. Of course, your method will end up better because having the daughter board means you can stick other stuff on it (eg. optoisolator).

It's probably not that hard to do but I'm a lazy b*stard ;) There you go, it can forever be known as: "The Lazy B*stard 4-Page EPROM" :cool:

I'll call mine the "Pointless 4 page Map with no car to put it in EPROM"

Still, it'll be ready for when I get one at this rate!

I'll order the bits next week and see how I get on with it.

Right, I said I'd stick some details up for how to wire the switch, so here we go...

 

This is what the back of your 6-pin switch should look like:

 

1 2

3 4

5 6

 

With the switch in the 'up' position, 1 and 3 are connected together, and 2 and 4. In the 'down' position, it's 5 and 3, and 6 and 4.

 

Start with the 3 wires coming from the 3 pin-20's of the EPROMs and the ECU socket. Wire the top EPROM to pin-2 of the switch, the bottom EPROM to pin-6 of the switch, and the ECU socket to pin-4.

 

Next, wire pin-28 of the EPROM pair (the 5V) to pin-3 of the switch. Run a couple of small wires across the switch between pin-5 and pin-2, and also join pin-1 and pin-6.

 

With the switch up, you'll select the top EPROM (and pull the bottom EPROM to 5V). With it down, you'll select the bottom EPROM (and pull the top EPROM to 5V).

It's been a while, but here's a pic...

 

PCB?! What's that then?

 

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