EER-018
Introduction to Digital Computers
Lecture 26
Instruction timing
For the 6805 chip, maximum internal clock freqeuency is 2.1 MHz.
Frequency, F = 2.1 x 106 1/s
Clock period, T = 1/F = .5 x 10-6 = 500 x 10-9
= 500nS = time of 1 cycle.
How long does the following loop take to execute?
CLRX
; 3 cycles
loop DECX
; 3 cycles
BNE loop
; 3 cycles
An example program - planning, documentation
Write a program that will read the state of an input switch connected to
bit 0 of port A. If the switch is pressed (a "1" is read on bit 0 of port
A) then we will turn on an LED attached to bit 7 of port A for about one
second, then turn it off until the button is released and pressed again.