I purchased a Tech Tools Econorom III emulator (www.tech-tools.com/er3.htm) . no magic here really. They have many different flavors, I picked the one that would do 512K proms (for no other reason than I thought maybe later in life I might need the additional space for another project, but not likely as I dont use these tools much if ever). This emulator has a 45 nS access time which is more than fast enough considering the prom that I was using was 120 nS. They do have more powerfull units, but for the DIY group that is never going to use this for anything other than this, I dont see a point in the more expensive one. I suppose that if you used it once a week, there might be some justification.
When I purchased mine (2001) it was $239.00 (US$). check thier web site for current pricing.
They have a few options one of which I opted for under the recomendation of the sales guy @ Tech Tools, this was the external power (click here for more information on the external power & comm cable). This is simply a wall wart that supplies the Emulator with +5 Vdc to power the emulator when the target (the ecm) does not have any power. I chose this more for insureance reasons than anything. The Sales person @ Tech Tools said that they have a number of customers that are using this for auto applications (but could not tell me what kind of cars) & for the most part they are finding that they get the most reliable performance when the emulator is powered by an external source (more on this later).
The Econo Rom 3 (ER3) suggests that you use the reset line on emulator to pull the reset line on the cpu during uploads of the new prom image (Click here to got the page with reset line information). this means that when you upload the new .bin file to the emulator it pulls the reset line on the ecm & stops it from accessing the rom. the idea is that you dont want the cpu trying to access the rom (or write to it) when it is uploading the new image. another important issue is that when it releases the reset line, the cpu will start up cold & that means that it is going to access the rom from the start & not from where it was when you uploaded the new image. depending on what it was doing it could get very confused. I tried to use the emulator without the reset line connected & ran into problems. what would happen was that after it loaded the new image into the rom it would not run on it. the motor continued to run but it was running in Limp Home Mode (LHM). I would then load the image in again 4 or 5 more times & it would take it. when I used the reset line, as Tech Tools suggested I got more reliable loads & it was more likely to continue to run.
Note on the reset line, even though I was getting what I considered good results with the emulator, there are small gotcha's. one is that when you are loading the image into the emulator the car wants to die. what I was doing was taking the car up to 2000 rpm, hitting the load button & loading the new image into the emulator. the car would sputter & try to die just in time for the ECM to start running on the new image. I did have about 5% of the time where the emulator would either not take the image or the car would not run on it. I just kept the RPM's up & reloaded the image into the emulator & it would load fine. I dont think that I have had to load an image into the car more than 2 times for it to take.
if you are using the 7730 ECM, I have pictures below that discribe what I did to mine to get the reset line connected (thanks to all on the GM-ECM web site that helped me with fingering this out). this was not that difficult once I figured out what line to connect it to & I stoped blowing up ECM's (my bad not the emulator). I figured that it was smarter to have an "emulator ecm" that was specifically for working on the prom (as they are cheap enough), so that I could work on it & even transfer it to another car & not have to worry about the reset line or anything plus as Mr. Plecan says, "Lets see how many Fel-pro or Accell guys can get an ECM for $40 on Sunday afternoon, so that they can get to work on Monday". if you are not using a 7730, goto Ludis' site (pay close attn on his site, there is SOO much information there you will miss it if you are not looking. just about anything GM ECM is there if you look long enough) & get the print for your ecm, see further instructions in figureing out what connection to connect it to.
Another Gotcha, is the Limp Home Mode. GM has a LHM that allows the car to run if there is a major problem with the prom or ECM or other issues relating to the EFI. this appears to be both good & bad. I think that during the loading of the new image, I think that the ECM has enough time to go into the LHM, I think that this is what causes the bad loads of the emulator. The emulator has a load & verify function or a load only. I have been able to reduce the load time & the reliability of the loads by turning off the verify function & only loading the image into the emulator. But on the flip side to the LHM, is that when it does not load, the car continues to run in LHM & allows me to load the image back in again.
NOTE OF CAUTION: I have not tried to load an image into the emulator while the car is rolling down the road. first of all, it is hard to see the road, hold the laptop, keep notes in your note book (YES, keep a note book) operate 3 different software programs & not crash. this is not an intelligent thing to do in my opinion. I would suggest that you record your data, pull over & inspect it. Update your notebook. Edit your bin & save it to disk. load the new bin into emulator & then go & test your edit. if you are running the car on a dyno, I suppose that there is a bit less going on but you are still going to have to pay attn to what you are doing. I assure you that the Dyno owner is not going to appreciate it if you hurt his equipment.