1280n development board serial port probs.

[cerickson]

I seem to be getting unreliable communications when trying to use the on-board serial line driver chip and J25/J26. I am simply trying to communicate with a (known to be good) PC serial port set up for 9600/n/8/1 w. no handshaking. Just using Hyperterm to look at received data (also no handshaking). I have J13 wired to COM2 (D.2/D.3). When I use an external MAX-232 style chip (HIN232CP), everything works fine. Most of the time there is no received communications but sometimes there is.

This is certainly something simple but I can't find the answer and I am willing to ask first before I start getting radical with experimenting on the hardware.

-Christopher Erickson

[dkinzer]

I seem to be getting unreliable communications when trying to use the on-board serial line driver chip and J25/J26.

Just to be clear, the J13 T and R pins are connected to the TTL side of the RS-232 converter and the corresponding RS-232 side is connected to J26. The T pin is an input and the R pin is an output.

It is possible that the spare section of the RS-232 converter chip is defective or there may be a solder bridge on the board or a similar defect. If you have an oscilloscope, you could connect it to pin 2 of J26 and continuously send a U character out Com2. You should see a square wave at the bit rate at about +/- 9 volts. Similarly, you could send U characters continuously from the PC and look at pin 3 of J26 and the R pin of J13.