Honored Contributor
Honored ContributorI'm not sure what source you are referring to (i.e., where the jbistub.c source code comes from), but if you are looking at a port that uses the parallel port, you have to realize that the 'classic' parallel port is output only at the DATA registers, and then input is obtained from either the CONTROL or STATUS registers. Those registers need to have their output drivers disabled by basically writing 1's to the port, so that an external signal can drive the pin low. Hence a line like:
write(com_port, &ch_data, 1); to port 1 could simple be deasserting the contol lines so that the TDO signal can be read. Just a guess ... Cheers, Dave
