Subject:
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Decoding Infrared receiver
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Tue, 2 Feb 1999 12:15:02 GMT
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Original-From:
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Tey Chee Beng <cbtey@singnet.com+saynotospam+.sg>
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Viewed:
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1259 times
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Dear Mr Fred Martin/Friends,
I have been playing with the handyboard for a while now, currently I have
four handyboards.
I'm working on the communication module between the handyboards using the
infrared emitter and the Sharp IS1U60 infrared demodulator. Currently, I
have this problem, I was unable to sample or decode the data from the Sharp
IS1U60 infrared demodulator, as the transmission part is OK.
The data transmitted from the infrared emitter is in the form of:
- 1 Start bit, 8 data bit and 1 stop bit, with a frequency of 400Hz/2.5ms
for 1 bit (for testing purpose).
As for the receiver part, the Sharp IS1U60 infrared demodulator is used and
is connected to the port PA2/TIC1. So the excepted data pulses received
after the Sharp IS1U60 infrared demodulator or at the port PA2/TIC1 will be
a low pulse (start bit), follow by the data (8 bits), and another low pulse
(stop bit). When there is no data, the port PA2/TIC1 will always read high
(logic '1').
(Codes written)
Interrupt will be generated when there is a falling edge detected on the
port PA2/TIC1, which is the start bit of the transmitted data. Upon
interrupt, 68HC11 will wait for 1.25ms, which is about the center of the
Start bit, and sampled the port PA2/TIC1 for the logic level (either a '1'
or a '0'). A logic '0' should be read from port PA2/TIC1, but that is not my
case, coz I always read a logic '1' at port PA2/TIC1. Does anyone know
what's the problem ?
The following codes is used to read port PA2/TIC1,
PORTA EQU $1000
CLRA
LDAB PORTA
STD PA2 (PA2 is a two bytes variable)
Even if I read the port PA2/TIC1 immediately in the interrupt subroutine, I
still get a logic '1' instead of a logic '0'. I have double check with the
oscilloscope that a logic '0' should be the correct value instead of a logic
'1'.
But with the Sharp IS1U60 infrared demodulator removed, and port PA2/TIC1
short to the ground, a logic '0' can be read.
What is the problem, does anyone ever faced the same problem before ?
Or is it because port PA2/TIC1 cannot handle a string of high frequency
pulses.
Any comments on this issue....
Thanks in advance,
James
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