IBM RT Series Hardware Reference Manual page 341

TNL SN20-9844 (March 1987) to 75X0235
Reset Adapter Register (Address X'OD20')
Note: After turning system power on, a write to this address is necessary to reset the adapter.
This is a write-only register and the data is of no significance. A write to this register resets the
adapter and acts just like the I/O channel signal 'Reset Drive'. This command initializes the
following registers:
Register Name Register Addr Register Data
X cursor register D9F800 0000
Y cursor register D9F802 FFFF
Queue counter register D9F804 0000
Scan line register
D9F808 0000
Mode shadow register D9F812 8090
Mode register ODIO I/O 8090
Control/status register OD12 I/O 0000
Graphic operation processing and command queue processing are stopped when this command
is executed. Also, the vertical and horizontal sync cycles are interrupted and video is disabled.
Disable DMA Processing (Address X'OD26')
This I/O address allows the system to disable DMA processing by the adapter. Data written to
this address is ignored.
Enable DMA Processing Register (Address X'OD28')
This I/O address allows the system to enable DMA processing by the adapter. Data written to
this address is ignored.
Extended Monochrome Graphics Adapter 29