Date   : Fri, 20 Jul 2012 23:17:13 +0100
From   : jgh@... (J.G.Harston)
Subject: RS423 won=27t transmit=2E Dead 6850?

Matthew Walker wrote:
> Interesting thing is, after trying JGH's 'very very dumb terminal'
> program the keypresses were echoed to the VDU. They were echoed to 
> the
> VDU even without the loopback, and even without the serial ULA in 
> place.

I've dug out the full Serial Port Tester program that I used to
carry around with me (careful, lines may have wrapped):

  10 REM > SerTester
  20 REM Test serial port
  30 :
  40 ON ERROR OSCLI"FX2":OSCLI"FX3":PRINTTAB(0,9):REPORT:PRINT" at 
";ERL;:END
  50 PRINT"Program has hung";
  60 *FX2,2
  70 CLS:PRINT"Serial Port Tester -- Press some keys:"
  80 PRINT'"Sending out:"'"Coming in: "
  90 PRINT'"Keyboard buffer:     ";FNempt(ADVAL(-1))
100 PRINT"Serial Input Buffer: ";FNempt(ADVAL(-2))
110 PRINT"Serial Output Buffer:";FNfull(ADVAL(-3))
120 PRINT'"If output buffer fills up and input buffer stays"'"empty, 
there's a problem with the serial port."
130 REPEAT
140   REM Wait for an entry to a buffer:
150   a1%=ADVAL(-1):a2%=ADVAL(-2):a3%=ADVAL(-3):IFa3%<>0 a1%=0
160   REPEATUNTILADVAL(-1)<>a1% OR ADVAL(-2)<>0 OR ADVAL(-3)<>a3%
170   IFADVAL(-1)<>0 AND ADVAL(-3)<>0 THEN 
B%=GET:PRINTTAB(13,2);FNh0(B%,2);" ";FNc(B%):OSCLI"FX3,7":VDUB%:*FX3
180   IFADVAL(-2)<>0 THEN 
OSCLI"FX2,1":B%=GET:OSCLI"FX2,2":PRINTTAB(13,3);FNh0(B%,2);" ";FNc(B%)
190   
PRINTTAB(21,5);FNempt(ADVAL(-1));TAB(21,6);FNempt(ADVAL(-2));TAB(21,7);FNfull(ADVAL(-3))
200 UNTILINKEY-1 AND INKEY-2 AND INKEY-3
210 END
220 DEFFNh0(A%,N%)=RIGHT$("0000000"+STR$~A%,N%)
230 DEFFNc(N%):IF N%=127 OR N%<32:="." ELSE =CHR$N%
240 DEFFNfull(N%):IF N%=0:="0 Full" ELSE =STR$N%+"     "
250 DEFFNempt(N%):IF N%=0:="0 Empty" ELSE =STR$N%+"      "

-- 
J.G.Harston - jgh@...      - mdfs.net