Model 4P RS232 problem

[BillB3857]

I have a Model 4P running LS-DOS 6.3.1. I set up serial communications between the 4P and my desktop. On the desktop, I run TeraTerm. My problem is, that once I establish communications UPPER case and lower case both work UNTIL I do something on the 4P that causes the "LS-DOS Ready " prompt. After that, all lower case characters that sent to my desktop are converted to extended ascii characters. The problem is repeatable. If I re-start my terminal program on the desktop, everything is normal UNTIL the LS-DOS Ready prompt on the 4P displays. Thinking I had a problem with TeraTerm, I dug out an old laptop running Win-98 and Hyperterm. Although the extended ascii symbols that are displayed instead of the lower case characters are slightly different, the symptoms are the same. Problem is somehow within the 4P. I then dug out a backup disk of LS-DOS thinking that something had garbled a data bit on the working disk. Results are the same. I've tried different baud rates with no change in the problem. I used "SETCOM (DEFAULD) on the 4P and reset the port on my desktop and still had the same problem. I used the "DEBUG" feature of TeraTerm to observe the HEX data stream during receiving the "LS-DOS Ready" and saw no abnormalities. I'm ready to pull my hair out and am looking for suggestion.

I should add, I use Link *ki *cl and Link *do *cl to establish the tie between the 4P and the desktop.

 

[BillB3857]

Found the problem!

Found the problem!

Well, I found the cause. Now all I need to find is an answer to it. I hooked my old Tektronix 308 data analyzer to the data stream and captured data. The 308 displays Hex, Binary and ASCII on one line for each character. It seems that when I was looking at the ASCII data stream, I started looking at the wrong point. I started looking at the "L" in LS-DOS. The character just before the "L" is an ASCII control character labeled "SO", or Shift Out. That character, from what I could find, is used to put printers/terminals into an alternate character mode for foreign languages, etc. TeraTerm defaults to a VT100 emulation and VT100 terminals have a pseudo graphic character set that the SO signal is turning on. So far, I haven't found a way to turn it off. As long as I don't do anything to cause LS-DOS to send its prompt to the screen, I'm OK.