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Dev board as external temp sensor?
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Author:  SaFeHeX [ Sat Sep 22, 2012 3:33 pm ]
Post subject:  Re: Dev board as external temp sensor?

Writing one's own software is deffinitely something i completely agree with for a multitude of reasons, however for reference purposes additional information can often be obtained from disassembly. Truth be told, at the time when i first got my hands on my first dev board, i didn't own a logic analyser and i couldn't beleive it when i found that CP was disabled. Although i have a Saleae these days, i've not even attempted to try it on a Dev board. Like many things, i just haven't got around to it.

Anyhow, i have just looked through the partial disassembly that i have (it was never fully completed) and it appears that a buffer starting at ram address 0x3F is filled with 3 bytes (not 5 as i had previously suspected) of 0xAA followed by two more buffer addresses adding the Synch word of 0x2DD4 (address 0x42 and 0x43 respectively) before the data payload.

Like i say, at this stage i have not used a logic analyser to confirm that all 3 bytes of preamble are actually being sent, they are just loaded into the ram buffer on the PIC. It could be that when the buffer is full and ready to send, the transmit routine may start the sequence from address 0x41 sending only one byte of preamble. This would give an easy option to modify it to 2 or 3 bytes of preamble if required, i guess to allow for reliability testing. Obviously the shorter the data packet then more battery power saved, even if only fractional.

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