Subject:
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Serial Line and Stop Switch
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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 22:48:06 GMT
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Original-From:
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Dan Wheeler - Boeing - Wichita Division <bdw0451@wbv1.bemsANTISPAM.boeing.com>
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Viewed:
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2126 times
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Hello,
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 but 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 cord 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, a low logic level near 4.5 volts and a high
logic level near 5 volts.
I've checked the 6811 E clock and it's still showing a 2 MHz square wave
(although 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
and before I do, 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 up to 4.5 volts? Has anyone run into
this problem 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 interest and support.
Dan Wheeler
(316) 526-5245
daniel.h.wheeler@boeing.com
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