Sorry about missing the subject tag, I completely forgot about it.

What you said makes sense, but when transmitting over actual wires instead
of IR, how does the USART signal a start bit and why doesn't it work the
same for IR?  I guess what I'm asking is how does the PIC know when I'm
sending a byte that starts with a 0 over the wires?  I'm using Async mode
so there is no clock pulse to signal a start.  Using only the five LSBs was
only because I cannot use all of PORTA's I/O lines because I am using an
external 20MHz ceramic resonator and the MCLR line is input only...this
leaves me with five I/O's to do output with.  The LEDs are simply for
debugging and testing this phase of my circuit.  I will need to send a
complete byte of data at a time once I get the IR part working.  Would it
be possible to use the 9 bit option and always have the 9th bit a 1 to
signal the start of a byte?  Then on the receiving end just disregard the
9th bit?  Thank you for your input, I appreciate the help.

Scott


At 08:55 PM 3/1/2004, you wrote:
>Added subject tag...
>
>
>>an LED graph.  Even though I'm sending a whole byte over serial, I'm only
>>actually using the five least significant bits of the byte.
>
>So how does the receiver know that when the first bit has been sent?
>
>For example, the receiver won't see any action at all until the
>transmitter tries to send a 1, right?  The receiver than takes that
>bit as the first of eight, waits the precalculated time period, interprets
>the next bit, repeat as needed.
>
>What you'll actually get is a left shifted version of the sent byte, which
>is shifted such that the first bit is the highest order 1 you wanted to
>send, followed by the remaining bits of the number and wrapped up
>with padded zeros.  For example, b'00011010' would be received as
>b'11010000',  b'00000011' would be received as b'11000000', and
>so on.
>
>The trick here is that you need to use some kind of alternate signal,
>bit-bashed out, or some very clever data manipulation with the UART.
>Either non-return-to-zero encoding, or pulse length encoding, or any
>of the other methods used by commercial products to communicate
>via IR can be used.  Snoop on Google for IR remote control PIC and
>you'll get some good ideas to start with.
>
>The simplest answer is to make the first bit of your data always 1,
>since you've indicated that that's a don't care bit anyway.  Thus,
>the first bit will always trigger a reception on the receiver's USART,
>and as long as the timing is good (which you have a strong indicator
>of, since wired serial works), you should be in business.
>
>Note that this is some speculation on my part, since I've never tried
>this, but I do know for sure that it's not too tough to emulate the
>Sony IR protocol, since I just made a receiver/transmitter pair that
>does just that!  That could be your fall-back method, but it requires
>more bit-bashing and what-not than using the USART.  Good luck!
>
>Mike H.
>
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