Subject:
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How to change the baud rate of Interactive C
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Sat, 15 Apr 2000 15:36:11 GMT
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Original-From:
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George Musser Jr <gmusser@hotmail.com+AvoidSpam+>
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Reply-To:
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georgejr@musser.comANTISPAM
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Viewed:
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1207 times
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Interactive C communicates with the 68HC11 at 9600 baud, but if you'd like
to change that -- say, to maintain interactivity over a slow RF link -- it
is easy to hack the software, at least in Mac version 3.1. I'm indebted to
Randy Sargent who sent me the C code for the relevant routine,
io_serial_init(). I was able to find the binary code using ResEdit. The
pcode also needs to be changed.
In ResEdit, open up the CODE resource and then the second block, ID=2.
Location 0x16D2 should read 0x6724, which is the branch corresponding to the
C code for switch/case 9600. Change this value to 0x6718 for 1200 baud and
0x6712 for 600 baud.
In principle, a value of 0x670C would allow 300-baud operation For 150
baud, you would also change the time constant for 300 baud, which is located
at address 0x16E2, from 0x017C to 0x02FE. (The time constant for 150 baud
does not appear anywhere in the Mac development environment, but this should
be the correct value according to the data sheet for the Zilog serial chip.)
I say "in principle" because whenever I try 300 baud or 150 baud, IC
crashes, which is a pity because the slow speed is useful for unpacketized
RF links. If someone can figure out why, please let me know.
The next step is to hack the pcode. Search for the following hex sequence:
0x1D 28 20 86 B0. The value 0xB0 is the time constant for the 68HC11's
UART. Change it to 0xB3 for 1200 baud, 0xB4 for 600 baud, 0xB5 for 300
baud, and 0xB6 for 150 baud.
There is one twist to all this. The baud rate of the pcode downloader is
fixed by the 68HC11 hardware. So you need to load the new pcode using an
unhacked version of IC and then switch to the hacked version for interactive
operation.
I'd be curious to hear about your experience with this, so please let me
know what happens!
George Musser
georgejr@musser.com
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