titus-larsen-titus-1981-apple-interfacing

entered and run, It first asks you for the period of each LED, in
onds, and then runs the program.
A = PEEK(49319)
INPUT "RED LED PERIOD ";Q
INPUT " GREEN LED PERIOD "; R
PRINT "TOTAL CYCLE PERIOD
POKE 49318,0
FORS = l TO Q
FOR T = 0 TO 780: NEXT T
NEXT S
A = PEEK(49319)
FOR S = l TO R
FOR T = 0 TO 780: NEXT T
NEXT S
GOTO 50
"; Q+R; " SECONDS"
hen the program is run, the time delays may be somewhat lengthed.
Why
e additional software steps (FOR S = 1 TO Q, FOR S = 1 TO R
d NEXT S ) , add time to the overall execution time of the proam,
although you will not see appreciable lengthening of the proam.
What does this program show you
illustrates many principles; the use of simple programs and simple
cuits to control external devices. It also illustrates the power of
SIC to control external devices through relatively simple software
ps. Remember, though, that BASIC is relatively slow.
ven though PEEK and POKE commands were used, the success
the Hip-flop interface did not depend on the actual transfer of any
or information. The flip-Hop was controlled, or switched,
ugh the use of device select pulses, alone. This principle is often
d when a control signal or control pulse is required, but no data
transferred.
lease remember that when a POKE command is used in the
SIC interpreter in the APPLE computer, a read and a write operaare
performed. Thus, if you choose to use a POKE command to
erate a device select pulse for control purposes, you must rememr
that the APPLE will a"lso perform a read from the same address.
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