James & Ili wrote:
>
> Marco,
>         Did you read the post by Danjel ? It looks like a simpler way to go.
> James

It appear to be the same approach except for the start bit detection.

The Danjel method detect the start bit "[using] a periodical interrupt
running at 2 or 3 times the baud rate" in witch you "samples the RX
line".
I just try to detect the start bit using an interrupt on the start bit
edge.
The rest of both methods is essentially the same.

There are pros and cons in both approaches:
Danjel method pros: you can use any pin as RX line because you sample it
using a bit test instruction. cons: if there is no traffic on the line
you still have 3 int per bit time interrupting you main task.
My method pros: your main task is only interrupted when a transmission
occur. If transmission are rare you can save lot of compute power. cons:
you have to use specific pin for the RX line. On the 16C84 you can
choose between the RB0/INT and RA4/T0CK1. Use the latter setting the
counter to external clock, no prescaler and preload it to 0xFF. At the
the first edge the counter roll to 0x00 thus generating an int. The
RB0/INT method is easier but the RA4/T0CK1 saves you an interrupt source
because you only use the timer/counter for bit timing/start bit
detection, having the RB0/INT free for other purposes.

The choice of the method used to detect the start bit depends completely
on your application and on the timing of your main task.

Marco

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