#: 6508 S12/OS9/68000 (OSK)
    04-Sep-90  17:33:36
Sb: ##pt68k & herc graphics
Fm: Ed Gresick 76576,3312
To: jack crenshaw 72325,1327 (X)


Hi Jack!

I don't use the mono adapter/monitor but I checked my handy-dandy IBM book and
found the following data for the Hercules Graphics Card. This information can
be found in pages 147 - 148 of 'IBM Microcomputers, A Programmer's Handbook' by
Sanchez and Canton published by McGraw-Hill.

    There is a warning:
         'INCORRECT PROGRAMMING CAN DAMAGE THE MONITOR'

The following is for the HGC Display Control Register at port 3B8H (write only)

    Bit 0 - 1
    Bit 1 - Mode Select - 0 = Text Mode
                          1 = Graphics Mode
    Bit 2 - 0
    Bit 3 - Video - 0 = Disabled
                    1 = Enabled
    Bit 4 - 0
    Bit 5 - Blink - 0 = On
                    1 = Off
    Bit 6 - 0
    Bit 7 - Graphics Page Select - 0 = Select page 0
                                   1 = Select page 1

    NORMAL SETTINGS:
                 Alpha mode: 00101001B = 29H
    Page 0 in graphics mode: 00101011B = 2BH
    Page 1 in graphics mode: 10101011B = ABH

 The following is for the HGC Display Status Register at port 3BAH (read only)

    Bit 0 - Video Signal State - 0 = Vertical Retrace
                                 1 = Scanning
    Bit 1 - Light Pen Flip-Flop
    Bit 2 - Not used
    Bit 3 - 0 = Dot not being written
            1 = Dot being written
    Bit 4 - Not used
    Bit 5 - Not used
    Bit 6 - Not used
    Bit 7 - Vertical Synchronization Signal - 0 = Raster in vertical retrace

 The following is for the HGC Configuration Switch at port 3BFH (read-write)

    Bit 0 - 1 = Graphics mode allowed
    Bit 1 = Access to page 1 allowed
    Bits 2 thru 7 - Not used

    HGC CONFIGURATIONS:
    00 = DIAG  (default)
    10 = HALF  (CGA compatible)
    11 = FULL  (text/graphics)

I hope the above information is of help.

Ed



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