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Printer Adapter Function
Description
The printer adapter portion of the IBM Monochrome Display and
Printer Adapter is specifically designed to attach printers with a
parallel-port interface, but it can be used as a general
input/ output port for any device or application that matches its
input/ output capabilities.
It
has 12 TTL-buffer output points,
which are latched and can be written and read under program
control using the microprocessor In or Out instruction. The
adapter also has five steady-state input points that may be read
using the microprocessor's In instructions.
In addition, one input can also be used to create a microprocessor
interrupt. This interrupt can be enabled and disabled under
program control. A reset from the power-on circuit is also ORed
with a program output point, allowing a device to receive a
'power-on reset' when the system unit's microprocessor is reset.
The input/output signals are made available at the back of the
adapter through a right-angle, printed-circuit-board-mounted,
25-pin, D-shell connector. This connector protrudes through the
rear panel of the system unit or expansion unit, where a cable may
be attached.
When this adapter is used to attach a printer, data or printer
commands are loaded into an 8-bit, latched, output port, and the
strobe line is activated, writing data to the printer. The program
then may read the input ports for printer status indicating when
the next character can be written, or it may use the interrupt line
to indicate "not busy" to the software.
The output ports may also be read at the card's interface for
diagnostic loop functions. This allows faults to be isolated to the
adapter or the attaching device.
Monochrome Adapter 11
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