Subject:
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Re: Extra output for clocking
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Mon, 30 Nov 1998 13:14:53 GMT
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Original-From:
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fthompson9@aol.comSPAMCAKE
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Viewed:
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2137 times
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Hugo Robertson:
One of the nice things about the 68HC11 chip is its well rounded timming
system. Grab your Handy board Technical reference manual and have a look at
page 48. PA0-3 are "Input Capture" pins. When the logic level changes
(according to the programmed level) this system time is captured and interrupt
flags set. The program can then tell exactly when something happened.
PA3-PA6 are "Output Compare" pins. Each of these pins can have a "time value"
assigned to them which causes them to change state. In addition there is a
master time value which will change the state of all desired pins. People use
these two registers to set the update frequency and duty cycle of this group
of pins to control servos (like the ones used in radio control airplains).
Using these timer pins you should be able to get clock signals into the
hundreds of kilohertz.
It looks like TOC3 is not being used, also TOC2 is going to the IR
transmitter and might be available. TOC5 goes to the piezo speaker, you
could use this if you either remove the speaker or put up with the noise.
You may be able to control this system with peaks and pokes. We will
need to hear from an Instant C guru to see learn how to handle the interrupt
flags. Just peaking at the flag registers may be enough, unless their
interrupt signal actually interrupts the CPU in which case you would need an
interrupt service routine. Any one care to comment on writing interrupt
service routines for IC?
hope this helps
Pherd
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