Subject:
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serial comm
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Mon, 3 Mar 1997 19:22:12 GMT
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Original-From:
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Daniel H. Wheeler <DANIEL.H.WHEELER@BOEING.COMavoidspam>
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Viewed:
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1608 times
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Good morning,
I am building a handy board for the first time using the Douglas
Electronics boards and parts from various sources. I have been following
the assembly instructions to the letter but am now stuck at the end of
section 4.4, Serial Line and Stop Switch.
I have successfully configured the main board to its bootstrap download
mode, but when I run the 6811 downloader software (DL.EXE PCODE_HB.S19
for DOS), the green SER LED on the I/C board blinks visibly, the green
PWR LED on the main board does not. I am using a new, two-foot long,
common telephone cable between the two boards.
I have hooked up the output of the MAX232 (pin 9) to an oscilloscope and
observed a nice serial NRZ signal with a low logic level near zero volts
and a high logic level near five volts, with the main board disconnected.
When I do connect the main board, the serial signal is still present at
pin 9 but its logic levels are clamped between 4.5 and 5 volts - that is,
the low logic level is near 4.5 volts and the high logic level is near 5
volts.
I've checked the resistors in the 6811's RxD path and am now faced with
replacing the 6811 itself as a last resort. Before I do, though, I have
two sets of questions:
1. Could anything else but a bad 6811 be causing the clamping of the
serial signal's low logic level to 4.5V? Has anyone run into this
before?
2. This is my first experience with PLCCs. Is there a simple, reliable
procedure for removing the 6811 from its socket without an expensive chip
puller?
Thank you very much for your consideration and support.
Dan Wheeler
(316) 526-5245
daniel.h.wheeler@boeing.com
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