Bit Map Memory Operations - IBM RT Series Hardware Reference Manual

Bit Map Memory Operations
The possible memory operations and respective mode bit definitions are as follows:
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 on-card write mask registers (WM1 and WM2).
It also initiates a write operation of the on-card 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 is
used to control 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 on-card data latches (D 1 ,D2,D3) to the bit map memory
making use of the rotate count, write mask, data mask, data bus and the logic unit. The following
operations must be completed prior to 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 110 'Store' to the adapter
control register.
System Read Operation (Mode
=
XX)
This operation reads 16 bits of data from the bit map memory and places it on the system data bus.
On-card data latches D 1, D2 and D3 are updated by this operation. Data is loaded into latches D 1,
D2 and D3 regardless of the setting of the mode. However, valid data is returned to the system
processor only if the mode is '00'.
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