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Hi Steven,<br><br>
Our posts have crossed so there's a later one with a corrected diagram.
The resistor on RXD0 ensures that no signal on the RS232 receiver will
interfere with the ISP when it is operating. The value is sufficient to
ensure isolation but not large enough to interfere with normal operation
when the ISP isn't active.<br><br>
It's a simple trick that I picked up from one of the very early Atmel
data sheets. They don't put that particular diagram in the data sheets
any more.<br><br>
There's a similar trick to be aware of when using SPI memory on AVR's
that use the SPI signals for programming. The SPI memory MISO signal can
become active when the chip select is floating during programming and it
can cause a programming failure. It needs either a 10k pull-up on the #CS
line or a 1k isolating resistor in the MISO line between the memory chip
and the processor. Again the ISP must be connected directly to the
processor pins.<br><br>
All the best for now,<br>
John <br><br>
<br>
At 16:06 12/03/2007, you wrote:<br>
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<font size=2 color="#000080"><a></a>Thanks John.<br>
<br>
What is the reason for RXD0 resistor? Haven’t heard about this one
before.<br>
How did you end up with the 1K value?<br>
<br>
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<font face="Times New Roman, Times" color="#000080"><b>Steven Lose<br>
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<font face="Times New Roman, Times" color="#000080">Software
Ingeniør<br>
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