TM 5-6675-323-14
a. Select code decoder and switch. The function of the select code decoder is
to determine when the interface is addressed by the calculator. The interface
responds only when the code on the peripheral address lines, PA through PA3,
R e c e i v i n g the preset code
matches the select code set on the select code switch.
e n a b l e s the interface to look for an I/O command from the c a l c u l a t o r . W h e n t h e
interface is ready for an I/O operation, the interface indicates its presence to the
c a l c u l a t o r by setting the flag line (FLG) low and setting t h e s t a t u s l i n e ( S T S ) l o w
when no error conditions exist on the interface.
b . I/O register decoder and calculator command register.
(1) The I/O register decoder is a network of gates which interprets the type
It determines whether the
of I/O operation being requested by the calculator.
transfer is an input or output operation by looking at the DOUT line. For an output
operation, the data on the calculator input/output data lines (IOD through IOD7) is
latched into the calculator output data register when the I/O strobe pulse (IOSB)
occurs.
For an input operation when the calculator is not conducting an interrupt
poll (INT), the data in the calculator input data register is placed on the calcula-
tor data lines.
F o r both input and output, the code on the DOUT, IC1, and IC2 lines
i s latched into the calculator command register when the I/O strobe pulse (IOSB)
occurs.
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