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)