Interrupts - Zenith Z-100 Reference Manual

Interrupts

The interrupts recognized by the system for the serial and parallel devices are
17H for the parallel I/O ports and 14H for the serial I/O ports. The following
operation codes, when placed in the 8088 AH register, will result in specific actions
as defined in the following paragraphs.
Parallel Port
Table 8.7 defines the results obtainable using an operational code followed by
an INT 17H instruction.
Table 8.7. Parallel Device Operation Codes
OPERATION CODE
Serial and Parallel Input/Output
DESCRIPTION OF ACTION
Print the next character in AL.
If the parallel device does not return a 'READY status
within a reasonable amount of time, AH will be set
to I, otherwise it will be 0.
Initialize the parallel port.
The returned AH value will contain the device status.
See code 2
Returns device status in AH as follows:
Bit 0 — Time out error, device not ready
Bit I — not used
Bit 2 — not used
Bit 3 — I/O error
Bit 4 — Device on line
B it5 — Outofpapersignal / ~)' ~
Bit 6 — Character admowledge
Bit 7 — Device is busy or in an error state
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