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HP 27130B
SIGNAL NAME
AO - A15
(Address Bus)
DO -
D7
(Data Bus)
M1-
(Machine Cycle 1)
MREQ-
(Memory Request)
IORQ-
(Input/Output
·Request)
Table 3-4. Z-80B CPU Signals
FUNCTION
Tri-state output, active high.
AO - A15 are a 16-bit address bus (AO is the
least significant bit).
This bus provides
address capability for up to 64K of memory data
exchanges, and for I/O device data exchanges.
I/O addressing uses the 8 lower address bits
to allow direct addressing of up to 256 input
or 256 output ports.
Tri-state input/output, active high.
DO -
D7
are an 8-bit bidirectional data bus
used for data exchanges with memory and I/O
devices.
Output, active low.
Indicates that the current machine cycle is
the OP code fetch cycle of an instruction
execution.
Tri-state output, active low.
Indicates that the address bus holds a valid
address for a memory read or write.
Tri-state output, active low.
Indicates that the lower half of the address
bus holds a valid I/O address for an I/O read
or write.
10RQ- is also generated with M1-
when an interrupt is being acknowledged.
Interrupt acknowledge operations occur during
M1 time, while I/O operations never occur
during M1 time.
3-10
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