💾 Archived View for uscoffings.net › retro-computing › systems › Tandy › t › ltport.txt captured on 2023-01-29 at 05:39:58.
⬅️ Previous capture (2022-06-04)
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Here are the bit assignments for the System status registers of
the 1400LT according to the service manual. I have been unable
to control any of the variables with port reads and writes
through DEBUG (which is not unusual, I think) and will try again
soon with a little assembly program. My special need is to switch
between RS232 and Modem in software. I can't guarantee the
accuracy of the data until I've fiddled with it a bit more. Good
luck to all the tinkerers . . .
System Status Register:
0F8H 0 Loop on POST
1 Co-processor installed (1=active; 0=not)
2 RAM size (manual unclear - I think means 00 = none,
3 RAM size 01=640, 10=512, 11=256).
4 Display 0 (00=reserved, 01= 40x25 color,
5 Display 1 (10= 80x25 color, 11= monochrome)
6 Number of floppy drives (00 = 1, 01 = 2, 10=3, 11=4)
7 Number of floppy drives
Write register
0FAH
0 LCD/CRT Exchange (1=CRT, 0=LCD)
1 FD Power control (1=on, 0=off)
2 LCD Power Control (1=on, 0=off)
3 EL Back light control (1=on, 0=off)
4 Keyboard select switch (1=external, 0=internal)
5 CRT Controller disable (1=DIS, 0=ENABLE)
6 Unused
7 Low battery 1 NMI Mask (0=MASK)
Read Register
OFAH
0 LCD/CRT Switch status (1=CRT, 0=LCD)
1 FD Power Status (1=on, 0=off)
2 LCD Power Status (1=on, 0=off)
3 EL Back Light Status (1=on, 0=off)
4 - 7 unused
Write Register
0FCH
0 Power save control (1=on, 0=off)
1 Modem power control (1=on, 0=off)
2 Modem/RS232 Switch (1=Modem, 2=RS232)
3 Speaker power control (1=on, 0=off)
4 Direct/Acoustic Switch (1=direct, 0=acoustic)
5 Clock speed exchange (1=7.16, 0=4.77)
6 Not used
7 Low battery 2 NMI Mask (0=MASK)