Question

Consider a computer system that contains an I/O module controlling a simple keyboard/printer Teletype. The following registers are contained in the CPU and connected directly to the system bus:
INPR: Input Register, 8 bits
OUTR: Output Register, 8 bits
FGI: Input Flag, 1 bit
FGO: Output Flag, 1 bit
IEN: Interrupt Enable, 1 bit
Keystroke input from the Teletype and output to the printer is controlled by the I/O module. The Teletype is able to encode an alphanumeric symbol to an 8-bit word and decode an 8-bit word into an alphanumeric symbol. The Input flag is set when an 8-bit word enters the input register from the Teletype. The Output flag is set when a word is printed.
a. Describe how the CPU, using the first four registers listed in this problem, can achieve I/O with the Teletype.
b. Describe how the function can be performed more efficiently by also employing IEN.


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  • CreatedMay 09, 2015
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