Memotech Limited MTX 500, Service Manual

Page: 19 / 78

15
IEI.
Interrupt Enable In (input, active High) is used
with IEO to form a priority daisy chain when there
is more than one interrupt-driven device. A High
on this line indicates that no other device of
higher priority is being serviced by a CPU
interrupt service routine.
IEO.
Interrupt Enable Out (output, active High). IEO
is High only if IEI is High and the CPU is not
servicing an interrupt from this Z-80 DART. Thus,
this signal blocks lower priority devices from
interrupting while a higher priority device is
being serviced by its CPU interrupt service
routine.
INT.
Interrupt Request (output, open drain, active
Low). When the Z-80 DART is requesting an
interrupt, it pulls INT Low.
M1.
Machine Cycle One (input from Z-80 CPU, active
Low). When M1 and RD are both active, the Z-80
CPU is fetching an instruction from memory; when
M1 is active while IORQ is active, the Z-80 DART
accepts M1 and IORQ as an interrupt acknowledge if
the Z-80 DART is the highest priority device that
has interrupted the Z-80 CPU.
IORQ.
Input/Output Request (input from CPU, active
Low). IORQ is used in conjunction with B/A, C/D,
CE and RD to transfer commands and data between
the CPU and the Z-80 DART. When CE, RD and IORQ
are all active, the channel selected by B/A
transfers data to the CPU (a read operation).
When CE and IORQ are active. but RD is inactive,
the channel selected by B/A is written to by the
CPU with either data or control information as
specified by C/D.
RxCA, RxCB.
Receiver Clocks (inputs). Receive data is sampled
on the rising edge of RxC. The Receive Clocks may
be 1, 16, 32 or 64 times the data rate.
RD.
Read Cycle Status. (input from CPU, active Low).
If RD is active, a memory or I/O read operation is
in progress.
MTX Service Manual