On Mon, 16 Apr 2007 04:37, you wrote: > Hi, > > > > I recently purchased a second-hand desktop (w/o the monitor) to use > > > as my development sandbox. > > > > <snip> > > > > What sort of cable are you using to connect from the USB adaptor to the > > desktop machine? If it is a straight-through one (even with a gender > > bender) it will not work. You need a null-modem, or at least a > > crossover on TX and RX pins. > > I have been connecting the USB adaptor directly to the desktop through > a gender bender.
Ok, well all that does is reverses the gender of the connection, making it physically possible to connect the DB9M at the end of your USB/RS232 adaptor into the DB9M on the desktop. It does nothing to the signal order. On a 9-pin serial port, pin 2 is data in to the PC, pin 3 is data out from the PC, and pin 5 is ground. If you connect two PCs directly (with a gender bender) then pin 2 on one PC is connected to pin 2 on the other, so clearly, neither PC will get data from anywhere. > Can I hope to purchase a null-modem at a Disk Smith Electronics store? > Is a gender bender necessary for all usb->serial adaptors? Dick Smith > doesn't have a null modem listed on their website. That certainly seems to be the case. Jaycar list two devices, but are not clear on the technical specs. You can often get away with just building yourself a cheesy adaptor- it'll certainly be adequate for testing, but later on you'll probably need to hook up all the other RS232 signals for handshaking etc. You will need two DB9F connectors and three pieces of wire. Basically you connect pin 5 on one connector to pin 5 on the other (i.e. straight through) and pin 2 on one to pin 3 on the other, and vice versa. You can see therefore, that data out from one PC is connected to data in on the other. The common ground (pin 5) is necessary so each PC has the same signal level reference. Your next problem, once you have determined that the USB/serial adaptor is working (see other email) and that you have built/procured a null-modem, is "What software is running on the desktop and responding to data coming in from the serial port?". If the desktop is running Linux then you might have a getty process listening on the serial port, so you *might* get a login prompt... Good luck, and have fun. A
