Zenith Z-100 Series, Technical Manual

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Page 2.9
PROG R A M M ING INFORMATION
Processor Swap Port (FE)
Processor swap is accomplished by the presently selected
processor writing to bit 7 of the processor swap port (PSP).
If a 1 is written, the 8088 is selected. A 0 selects the 8085.
(See the following chart.)
When the processor swap occurs, the newly selected proces-
sor can be restarted where it left off, or, an interrupt (l1 on
8259A) can be generated. Interrupt generation is enabled by
writing a 1 to bit 1 (not LSB) of the PSP.
The last option that concerns the swap port is the masking
of interrupts. If interrupts are not m asked, the c urrently
selected processor is signaled when an interrupt is requested.
If the MASK mode is selected, no interrupts will get through
to the 8085. The 8088 will service all interrupts. In the MASK
mode, a processor swap to the 8088 is generated whenever
an interrupt occurs with the 8085 active. MASK is bit 0 of
the PSP. A 1 activates this function.
Port
Address D 7 D6 D5 D4 D3 D2
D1 DO
FE
0 = Select 8085 processor
1 = Select 8088 processor
0 =
Both processors receive interrupts.
1 = Force a processor swap to 8088 if 8085
0 =
Resume execution from previous address
1 =
Force an interrupt (I1 of master 8259A) as
newly selected processor becomes active
is active