ACT apricot - Page 184

PARALLEL INTERFACE
Fault Input signal. Logic low state indicates a printer
fault condition.
Select Input signal. Logic high state indicates the
select status of printer; logic low the deselect
status.
ACK Input signal, Acknowledge. Logic low state
indicates that the printer is ready to receive
more data.
Busy
Input signal. Logic high state indicates that the
printer is unable to receive any data.
The three printer inputs, Fault, Acknowledge and Busy
can generate an interrupt request to the CPU by
programming the SIO and interrupt controller. The SIO is
. also able
to produce an associated interrupt vector
internally, to indicate the cause of the interrupt. The
system software can then determine the cause of the
interrupt and the required service routine, by using data
available from the SIO and data on the printer status lines.
System Control Interface
Port B and one input to Port C of the PIO form the system
control interface between the processors and other areas of
hardware
on the System Board. The system control lines are
defined below.
PBO Reset to CRT control. Active state, logic low.
When active, inhibits the production of the
display address information and video timing
signals, and clears the display address counters
to zero count state.
PB2 HLD to floppy disk drives. Active state, logic
high.
When active, engages the read/write head
of the selected disk drive against the disk.
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