TM 5-6675-320-14
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, PAØ through PA3,
matches the select code set on the select code switch. Receiving the preset code
enables the interface to look for an I/O command from the calculator. When the
i n t e r f a c e i s r e a d y f o r a n I / O o p e r a t i o n , t h e i n t e r f a c e i n d i c a t e s i s p r e s e n c e t o t he
calculator by setting the flag line (FLG) low and setting the status line (STS) low .
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
of I/O operation being requested by the calculator.
It determines whether the
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 (IODØ 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 -
t o r d a t a l i n e s .
For both input and output, the code on the DOUT, IC1, and IC2 lines
is latched into the calculator command register when the I/O strobe pulse (IOSB)
occurs.
4-137
