Mcgee, Mark wrote :

> Hi
> 
> I'm doing very simple RS232, no hardware or s/w flow control, 
> 8-bit bytes and
> 1 stop bit, and hence I intend to use D9 connectors and cables.

Yes, absolutly no need to go to DB25...

> 
> What is the correct cable and connector to use?
> 
> i.e. the PC serial port is always male, so the PC cable end 
> will need to be
> female.  What should my application end be, female?

Connector : female.
Cable : male.

> 
> I notice Wouter's Wisp628 *doesn't* use a null-modem cable, 
> but a male-female straight through cable.

Since the Wisp628 is (defined as) a DTE, yes.

> Is this what I should be using also? 

Yes, why not ?

> Obviously, the
> PC rx will go to PIC tx, and PC tx to PIC rx?  The crossing 
> will be made a the PIC circuitry end?

The crossing is defined in the "standard". Just wire-up your
DB9 in the "right way", and everything should be fine.
I think that calling this "crossing" might just be confusing.

> 
> I vaguely remember there being guidlines about DCE-DTE and 
> DCE-DCE cables etc,
> but I forget what's supposed to be what.  I assume my PIC 
> base temperature
> unit should be counted as a DTE (data terminal equipment)?  
> IIRC DCE-data
> communications equipment - i.e. modem?  So I'm doing DTE-DTE 
> comms......

Well, it's more or less up to you if your temp-cntr is a DCE or
a DTE. I'd say that it's easier to concider anything that is not
a PC (or other "computer") a DCE. No matter if it's a modem, 
printer or maybe a temp controller. I'd guess that a standard
DTE/DCE (male/female) serial cable migt be a little easier to find,
and in more different lengths.

"Null-modem" cables are used in some special cases, such as
when connection two PCs using the serial ports. And there are
also those small "gender-changers" in both DB9 and DB25 that
could be used for this.

If you need an odd-lenght cable, just wire up one ourself.
With no hardware handshaking, you need just three lines, but
you might have to "loop" a few pins at the PC side. Or maybe
not, depending on how the COM port is set up...

Regards,
Jan-Erik.

_______________________________________________
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist