ACT apricot - System Connections

SERIAL INTERFACE
System Connections
DO to D7 Data bus, used to transfer data and commands
between the processors and the SIO.
IORQ
Input/Output Request. Control input, active
state logic low, derived by combining the read
and write commands from the system control
bus (AIOWC and IORC) using an AND gate.
Used in conjunction with RD and the address
inputs B/A, C/D and CE to control the transfer
of data and commands between the SIO and the
procesors. An active state on IORQ indicates a
transfer operation on the data bus; RD signifies
the direction of data transfer (see below). IORQ
also has another function, when set active at
the same time as M1 is set active. This
condition acts as an acknowledgement of a SIO
interrupt, causing the SIO to release an
interrupt vector onto the data bus.
M1
Machine Cycle 1. Control input, active state
logic low. Function as described above.
RD Read. Control input. Used in conjunction with
IORQ and the address inputs B/A, C/D and CE
to control the transfer of data and commands
between the SIO and processing elements. If
both IORQ and RD are set low and a valid
address
is set up, the direction of datal
command transfer is from the SIO (read
operation). If IORQ is set low and RD is set
high, with a valid address set up, the direction
of data/command transfer is to the SIO (write
operation).
CE
Chip Enable. Address input, active state logic
low.
When active, indicates that the SIO is
selected for a data/command transfer
operation.
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