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Memory and I/O Usage
Port B
Write
7
6
5
4
operations
Bit 0
Bit 1
Bit 2
Bit 3
Bits 4-7
Read
7
6
5
4
operations
Bit 0
Bit 1
Bit 2
Bit 3
Bit 4
Bit 5
Bit 6
Bit 7
5/8 LS PRO HARDWARE TECHNICAL REFERENCE
3
2
1
0
speaker gate
speaker data
enable parity check
enable I/O check
refresh detect
timer 2 output
I/O check
parity check
Setting this bit to 1 enables the timer 2 gate. Setting this bit to 0 disables
the timer 2 gate.
Setting this bit to 1 enables speaker data. This bit is set to 0 during a
system reset.
Setting this bit to 0 enables Parity check. This bit is set to 1 during a
system reset.
Setting this bit to 0 enables an I/O check. This bit is set to 1 during a
system reset.
Reserved
3
2
1
0
speaker gate
speaker data
enable parity check
enable I/O check
refresh detect
timer 2 output
I/O check
parity check
A read operation returns the result of the last write operation to this bit.
A read operation returns the result of the last write operation to this bit.
A read operation returns the result of the last write operation to this bit.
A read operation returns the result of the last write operation to this bit.
This bit toggles on each refresh request.
This bit reflects the condition of the timer 2 output latch.
This bit reflects the condition of the I/O check latch. If the bit is set to
1 an I/O check has occurred.
This bit reflects the condition of the Parity check latch. If the bit is set
to 1 a Parity check has occurred.
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