Interface Signals - Printronix p300 Maintenance Manual

SIGNAL
Received from Host Computer
IDB1 – IDB8
IPI
ICSTB
IDSTB
Sent to Host Computer
IDR
IONL
IRDY
ICPE
ICBY
IACK
P300/P600 Principles of Operation
Table 2–2. Interface Signals
DESCRIPTION
Seven bit character or control code, with bit 8 used to select
optional character set (performing the same function as the
shift out code SOV). If bit 8 is not used, jumper W4 must
be present to disable the bit.
Bits 1 through 7 pass through receivers and polarity logic to
latches for storage until transfer to the printer buffer.
Paper instruction signal asserted by a Dataproducts compatible
host computer when the code on the data lines controls the
EVFU and is not loaded into the printer buffer. PI is applied
through polarity logic and stored in a latch along with the code
on the data lines. If PI is not used, jumper W5 must be in–
stalled to disable the line.
Data strobe generated by Centronics compatible host computer.
IDSTB is received and applied through polarity logic to strobe
timing circuits and to latch circuits which are loaded by the lead–
ing edge of the pulse.
Data strobe generated by Dataproducts compatible host
computer. IDSTB is received and applied through polarity logic
to strobe timing circuits and to latch circuits which are loaded by
the leading edge of the pulse. With jumper W2 installed, the
trailing edge of the strobe loads the latches. Data, function
codes, and the PI bit are loaded by DSTB.
Data Request signal sent to Dataproducts compatible host
computer. When IONL is true, printer is in buffer load state,
and input latches have been cleared and are ready to accept the
next character.
Online signal set when operator presses ON LINE switch to
make printer able to accept data. Sent through polarity logic
and a driver circuit.
Ready (RDY) signal sent when online has not been set but
printer is otherwise ready to receive data. RDY is sent through
polarity logic and a driver circuit to the IRDY line. RDY also
appears on the ICPE line (bypassing polarity logic) for use by
a Centronics compatible host computer.
"Not ready" signal conditioned for a Centronics compatible
host computer.
Busy signal indicates to the host computer that the printer buf–
fer is not available to receive data.
Acknowledge signal sent to a Centronics compatible host com–
puter, through a driver circuit, to request the next character.
Set when ICBY is negated or when ON LINE switch is pressed.
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