Subject:
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Handy Board Assembly
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Wed, 5 Mar 1997 17:21:49 GMT
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Original-From:
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Daniel H. Wheeler <Daniel.H.Wheeler@Boeing+antispam+.Com>
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Viewed:
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2411 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 with great success up to now: I'm 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; however, 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,
but 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 (pin 9) of the MAX232 to an oscilloscope with
the main board disconnected from the I/C board. I observed a nice serial
signal with a low logic level near zero volts and a high logic level near
five volts. When I connect the main board and observe the signal at the
same pin on the MAX232, I see logic levels clamped between 4.5 and 5
volts - that is, low logic level near 4.5 volts and high logic level near
5 volts.
I've checked the 6811 E clock and it's still showing a 2 MHz square wave
(with ringing due to wire probe leads, probably) as well as the resistors
in the 6811's RxD path. My last resort is to replace the 6811. Before I
do, though, I have two sets of questions:
1. Could anything else except a bad 6811 be causing the clamping of the
serial signal's low logic level to 4.5V? Has anyone run into this
problem before now?
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 interest and support.
Dan Wheeler
(316) 526-5245
daniel.h.wheeler@boeing.com
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