Bit Map Memory Operations - IBM RT Series Hardware Reference Manual

Bit Map Memory Operations
The following are possible memory operations and respective mode bit definitions.
System Write Operation (Mode
=
00)
This operation writes 16 bits of external data to the bit map memory at the address specified in the
system processor 'Store' instruction.
Overlay Write Operation (Mode
=
01)
This operation writes 16 bits of external data to the onboard write-mask registers (WMI and
WM2). It also initiates a write operation of the onboard system data latches to the bit map memory
at the address specified in the system processor 'Store' instruction. The new value in the write mask
controls the write to the bit map. This operation will not affect the contents of the system data
latches. Preloading the system data latches with the proper constant makes it possible to 'AND' or
'OR' system data with the bit map memory in one memory operation.
Adapter Write Operation (Mode
==
10)
This operation writes data from the onboard data latches (D 1 ,D2,D3) to the bit map memory using
the rotate count, write mask, data mask, data bus and the logic unit. The following operations must
be completed before executing this operation:
• Load the data latches using an adapter read operation.
• Load the write mask using an overlay write operation.
• Load the operation mode, rotate count and logic function using an I/O 'Store' to the adapter
control register.
Advanced Color Graphics Display Adapter 5