First post here (sorry it's quite a length one). Here's the problem - I have two USB to serial adaptors (identified as using the Prolific PL-2303) which *aren't* identical in appearance but appear the same when detected by OS's. I would like to be able to identify them through software without having to know which adaptor is plugged into which USB bus or whatever. If serial device X is connected to adaptor X and serial device Y connected to adaptor Y, when in linux the kernel can detect an assign these USB devices different device names between reboots. I've compared the devices in Windows Device Manager, and also with 'lsusb -v' in linux and there's little to distinguish between them. I've read the following thread from this forum about being able to reprogram the EEPROM - edaboard.com/thread62529.html - however for adaptor 1 if I leave the eeprom writer program settings as default, change the serial number or the PID and press write, I get an error message 'Compare EEPROM failed!'

Posted: 2004-10-29 19:24 i want the eeprom writer from prolific. Windows Driver Installer Setup Program (For PL2303 HXA, XA, HXD, EA, RA, SA. Prolific offers complete USB to Serial/UART/RS232 and USB to Printer interface. Driver Download; Windows: PL2303 EEPROM Writer Program (HXD/EA/TA).

Followed by an alert 'Write EEPROM successful!' But it clear isn't as the PID hasn't changed and (although I'm not certain I know where to look for the serial number) the serial number doesn't appear to change either when reviewing device info (nothing seems to change). Adaptor number 2 - the first time I got it out the box and tried to write to the EEPROM using the writer (same defaults, but just changing the serial number) and didn't get the error message, just the success one! However I don't see anything in either OS that relates to the serial number I supposedly wrote to the device.

Since that first time of using the EEPROM writer with that device, I get exactly the same behaviour as adaptor 1 when writing. When trying to read the EEPROM I get the alert message 'The EEPROM isn't programmed yet!' , confirming the previous writes don't seem to have done anything. I've also read jethomson.wordpress.com/2010/02/21/diy-usb-to-serial-cable-for-3usd/ which in the last two paragraphs mentions the following from the blog owner: 'I looked into this, but my memory is a bit hazy on the details.

IIRC you need a special USB board that puts out 6V to program the EEPROM in the rev. Symantec.ghost.11.5.corporate.dos.boot.cd.iso. D, and it can only be programmed once. A has a 2-wire EEPROM interface though, and I think if you program an external EEPROM correctly you can tell the PL2303 to report itself as High Power device and therefore get 500 mA from the USB port. I keep meaning to try this but never have.

If you get it to work, write back and let us know!' I've also emailed Prolific to ask for access to their versions of the EEPROM writers as one of their product sheets for the 2303 suggests that EEPROM writers between the different versions of the adaptors (X, HX etc) aren't compatible. No response (been about a week now).

If anyone has any info to help with this, it would be greatly appreciated - seems I'm running out of things to try. First you should make sure you can't differentiate the two devices by serial number. If not then you should figure out which chip you have. If it is PL-2303HX rev. D, the EEPROM writer program (1.0.0.3) you have won't work. The PL-2303HX rev.

D has an _internal_ one time programmable ROM (OTPROM). You need a special 5 to 6.5V adapter to be able to program it. The EEPROM writer (1.0.0.3) uses the PL-2303 to write USB descriptors to an _external_ EEPROM. You might not have an EEPROM connected to the PL-2303. I know my USB to serial adapter doesn't have one.