serial_sw should allow only transmit or receive without pin definitions

[GoogleCodeExporter]

When communicating with devices having only transmit pins, user is forced to 
assign a transmit pin too, even if its not required. Results in " 
"serial_sw_tx_pin" not defined".  Can isdefined be used to avoid the transmit 
pin usage in serial_sw library ?

Original issue reported on code.google.com by sunish....@gmail.com on 23 Jul 2010 at 3:10

[GoogleCodeExporter]

Of course this is possible. 
An other way to achieve the same is to define:
var bit serial_sw_tx_pin
This satisfies the compiler and all related code is removed by the optimiser if 
you do not call is.
I thought this was in the documentation, but it seems not to. Maybe we should 
extend the documentation?

Original comment by jsu...@gmail.com on 23 Jul 2010 at 5:20

[GoogleCodeExporter]

I didn't think of the declaration you mentioned.It would be easier for the 
user, if default is defined as "if not used no declaration needed". Yes 
documentation too should be updated.

Original comment by sunish....@gmail.com on 23 Jul 2010 at 5:52