Read non-standard serial data via parallel port

[mpitts at vnet.ibm.com]

I'm looking for some advice on how to read some non-standard serial
data from an automotive ECM.  I have the necessary cable rigged up
already to get the data into the parallel port.  I've taken some
samples of the data and here's what I've seen:

      --    -    ---                 -   ---     --
     |  |  | |  |   |               | | |   |   |  |
     |  |  | |  |   |               | | |   |   |  |
     |  |  | |  |   |               | | |   |   |  |
     |  |  | |  |   |               | | |   |   |  |
     |  |  | |  |   |               | | |   |   |  |
     |  |  | |  |   |               | | |   |   |  |
     |  |  | |  |   |               | | |   |   |  |
     |  |  | |  |   |               | | |   |   |  |
-----    --   --     ---------------   -     ---    --------------
                         1300 #                          1300 #
     |<-- 300 # --->|               |<-- 300 # --->|


The numbers represent the number of times I was able to perform a
loop in the polling program.

I'm assuming the 1300# states are interbyte spacings and the
300# areas are the actual bytes.  The smallest count between
transitions was was ~30#, which would indicate my bytes are
10 bits long (start and stop bit perhaps).

I know I can read the data stream with polling loops, but
would like my routines to be CPU independent.  The data comes
in on the -ACK line of the port, so I can use an ISR if
necessary.

Anybody have any hints/clues, or better yet, code snippets.

Thanks,

Mike Pitts                         mpitts at vnet.ibm.com
Software Engineer                  (407) 443-8941
IBM Wireless Data Division
Boca Raton, FL