Ive wondered this lately..

I've used my Mastach cable to read data from ALDL before.. Works fine.

I've read that you can program the 16188051 PCM through the ALDL port. I'm curious as to how this is possible, seeing that the specs on the port have just 1 pin that goes to a pin on the PCM labeled serial data. How can receive and transmit be done on the same pin?

Does anyone know the concept? Also the references i can find online to cables show just 1 pin connection aside from GND. How can the computers serial port communicate both ways on one pin?

The only thing I can think of or guess is that the computer is connected to the ALDL using a pin that the computer is capable of switching and switches the pin in certain sequences, like morse code and certain sequences specify that the next bit will be sent data rather than received data.

I am just curious how this all works, that you can program a PCM and read data from it, using just one pin. Does anyone have an understanding or confirmation on how this works?

Thanks
-Randy

I cant answering your question b/c i dont know that much, but from all the DIY Prom reading i have done, i have came up with some results about handshaking. From what i can make of it, is what i qouted you about above. Do a www. search on handshaking serial and etc. Good luck

kind of like binary pulses?

the ecm waits for something until it receives a request from the scanner. After the scanner sends the request it waits for a response. It is uni-directional.



I've noticed that sending any requests to the ecm is echoed back to the computer due to the 1 wire setup, but its not a big deal.