Z8018x Family
MPU User Manual
9
BUSREQ, and INT0 signals are inactive. The CPU acknowledges these
interrupt requests with an interrupt acknowledge cycle. Unlike the
acknowledgment for INT0, during this cycle neither the M1 or IORQ
signals become Active.
IORQ. I/O Request (Output, Active Low, 3-state). IORQ indicates that
the address bus contains a valid I/O address for an I/O read or I/O write
operation. IORQ is also generated, along with M1, during the
acknowledgment of the INT0 input signal to indicate that an interrupt
response vector can be placed onto the data bus. This signal is analogous
to the IOE signal of the Z64180.
M1. Machine Cycle 1 (Output, Active Low). Together with MREQ, M1
indicates that the current cycle is the Op Code fetch cycle of an
instruction execution. Together with IORQ, M1 indicates that the current
cycle is for an interrupt acknowledge. It is also used with the HALT and
ST signal to decode status of the CPU machine cycle. This signal is
analogous to the LIR signal of the Z64180.
MREQ. Memory Request (Output, Active Low, 3-state). MREQ indicates
that the address bus holds a valid address for a memory read or memory
write operation. This signal is analogous to the ME signal of the Z64180.
NMI. Non-maskable Interrupt (Input, negative edge triggered). NMI has
a higher priority than INT and is always recognized at the end of an
instruction, regardless of the state of the interrupt enable flip-flops. This
signal forces CPU execution to continue at location 0066H.
RD. Read (Output active Low, 3-state). RD indicates that the CPU wants
to read data from memory or an I/O device. The addressed I/O or memory
device must use this signal to gate data onto the CPU data bus.
RFSH. Refresh (Output, Active Low). Together with MREQ, RFSH
indicates that the current CPU machine cycle and the contents of the
address bus must be used for refresh of dynamic memories. The low order
8 bits of the address bus (A7–A0) contain the refresh address.
This signal is analogous to the REF signal of the Z64180.
UM005001-ZMP0400
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