RS232... here goes!

[jac_goudsmit]

banedon wrote:

I am using a 'scope, but the signals were solid.
BTW do I need to use a null modem cable? Mine is straight through...

You wired your project up as a DTE. A PC is also wired up as DTE so you will need a null modem cable, yes.

Normally a full null modem connection between two RS-232 ports that us all signals, uses these connections:

TXD -> RXD
RXD <- TXD
RTS -> CTS
CTS <- RTS
DTR -> DSR and DCD
DSR and DCD <- DTR
GND

RI can stay disconnected on both ends.

The PC uses a female DB-9 connector, and so should your project, if they are DTE wired (i.e. RXD on pin 2, TXD on pin 3). Your straight wire has a male DB-9 and a female DB-9, but a null modem adapter or cable has two male DB-9 connectors.

When nothing is transmitted or received, you should measure between -3 and -12V on all pins except GND and RI. If not, something is disconnected or connected wrongly, or your cable doesn't have wires on all pins or the PC on the other side doesn't have CTS/RTS and/or DSR/DTR implemented. In that case, you can use a null modem that connects fewer wires and has loopback wires. Google for "null modem cable" for more info.

NB: DTE=Data Terminal Equipment, i.e. a terminal or a computer; DCE=Data Communication Equipment, e.g. a modem.

===Jac

[banedon]

Thanks Jac. I did have things miswired, although I'm still having issues so will wait until the weekend and then go through everything bit by bit. I'll keep what you've said regarding the signals in mind when I do.
I also have a standard DB9 to DB9 null mode cable and USB to DB9 null modem cable on the way to me courtesy of ebay.

[floobydust]

For null modem cables, I found these on Mouser... DB-9 at each and a full null modem configuration. I've been using these with a pair of my 65C51/Max238 interface boards.

http://www.mouser.com/ProductDetail/Tri ... IenA%3d%3d

I also use one of these connected via USB to a Win7 64-bit Virtual Machine running ExtraPutty. The device gives you two RS-232 ports from a single USB connection. I'm able to run two concurrent terminal sessions to two 65C02 boards.

http://www.mouser.com/ProductDetail/FTD ... ZMOg%3d%3d

[banedon]

I'll have to save up for those, floobydust, but I'll be sure to invest next month.

In the meantime, I've received my 9pin to 9pin null modem cable and also the USB based one. I'm now seeing some activity on pin 2 (RXD) when I tap a key at the PC end, but nothing is coming back.
Pin 3 (TXD) is at about -8V all the time. So I still need to beat with with a hammer a bit more .