Interfacing Examples; Sample Program System - RCA COSMAC Operator's Manual

INTERRUPT (cont'd)
The source of an asynchronous interrupt must be
deduced from externally-generated information,
such as the contents of an interrupt status regis-
ter (interrogated by an I/O READ instruction), any
external flag values or the address of register RO
as dictated by DMA activity. The presence of a
programmab Ie INTERRUPT ENABLE bi t in th'e COSMAC CPU
simplifies the process,of analyzing and servicing
interrupts.
INTERFACING EXAMPLES
Sample Program System
Pages 60 to 64 of the COSHAC Microprocessor
Manual describe the implementation of a pro-
grammed sequencer hased on the COSMAC micro-
processor. The description there outlines the
required external logic and the associated
control program. The program uses an I/O
Read instruction to read data from switches
and an I/O Write instruction to send data to
an "output register". External flag #1 is
coupled to the "enter switch". We will show
here the logic required to implement the same
system within the Microkit environment. The
Byte I/O module will be utilized. We assume
that the required interface logic to be added
will reside on a user-supplied card occupying
plug-in position 22.
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