Interrupt Controller (8259A)
RR
The RR bit is used to execute the read register
command. If RR is set to 1, the read register command
is issued and the state of RIS determines the register to
be read. If RR is 0, the read register command is not
issued.
P
The P bit is used to issue the poll command. If P is set to
1, the poll command is issued. If it is 0, the poll
command is not issued. The poll command overrides a
read register command if they are set simultaneously.
SMM
The SMM bit is used to set the special mask mode. If
SMM is set to 1, the special mask mode is selected. If it
is 0, it is not selected. The state of the SMM bit is
honored only if it is enabled by the ESMM bit.
ESMM
The ESMM bit is used to enable or disable the effect of
the SMM bit. If ESMM is set to 1, SMM is enabled. If
ESMM is 0, SMM is disabled. This bit is useful to
prevent interference of mode and command selections in
OCW3.
12-20