Copyright(C) 1994,1995,1996,1997 Terumasa KODAKA, Takeshi KONO


■High resolution switching control
Subject           High resolution normal dual use model PC-9821A-E02
Explanation     o In high-resolution/normal mode models, several I/Os are used to switch between high-resolution mode and normal mode.
Relation          0000:0501h bit 3


I/O               0431h
Name              Hi-Res/Normal switching switch reading
Undocumented
Subject           PC-9821Ap･As･Ae
Function
                  [READ]
                  bit 7~3: unused
                  bit 2: High resolution/normal selection switch
                         1=Normal mode side
                         0=High resolution mode side
                  bit 1,0: unused

Function        o Reads the status of the high-resolution/normal switch. Effective even when the high resolution board (PC-9821A-E02) is not installed.
                o In the PC-9821Af/Ap2/As2/An/Ap3/As3, this I/O does not exist because this setting is done software-wise using the system setup menu.
Relation          I/O 0CA0h


I/O               0467h
Name              High resolution mode notification
Undocumented
Subject           High resolution normal dual use model
Function
                  [READ] None

                  [WRITE]
                  bit 7～2:Unknown
                  bit 1: High resolution mode flag 1=High resolution 0=Normal
                  bit 0:Unknown

Explanation     o An expansion board (for example, a SCSI board) that needs to distinguish between normal mode and high-resolution mode decodes this I/O
                  and monitors the value that ITF outputs to this I/O at reset, and selects high-resolution mode. Determine whether it is in the mode.


I/O               0CA0h
Name              Hi-res board detection
Undocumented
Subject           PC-9821Ap･As･Ae･Af･Ap2･As2･An･Ap3･As3 + PC-9821A-E02
Function
                  [READ]
                  bit 7～1: unused
                  bit 0: Hi-res board detection
                         1=No high resolution board
                         0=High resolution board available
                         * Before detecting the high resolution board, output 00h to this I/O in advance.

                  [WRITE]
                  bit 7～0: Preparation for high resolution board detection
                            * Prepare to detect high-resolution boards by writing 00h.

Explanation     o Check whether the high resolution board (PC-9821A-E02) is installed. u Window accelerator board A, full color window accelerator The Windows
                  display driver for boards A and A2 checks whether there is a high-resolution board in order to pass the video output from the window accelerator
                  through the high-resolution board, and confirms that the high-resolution board is installed. In this case, control the high-resolution board's
                  video output switching relay.
Relation          I/O 0431h■[PC-9821Ap･As･Ae]