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PICList Thread
'M-bus master'
1997\05\16@091245 by Antonio Almeida

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Hello people, i want your opinion in this problem of mine. I need to
convert the variation of current in a line to data bits (it's the way the
M-Bus works).
The current in the bus is Ii (grafic below), this is the idle current
(might change a little), when a slave drives the bus the current will rise
to Io (the difference is known).

                       .
                      / \
                       |
                       |
                    Io |     ----       ----
                       |    |    |     |    |
                    Ii |----      -----      -----
                       |
                        -------------------------->
                                                  t

I want to use the built in UART so i think it's ok to use something like
this:


                           |                   ------------
                           |                  |            |
                     .     |-----             |  PIC16C73  |
                    / \    -     |            |            |
                     |    | |    |__|\        |            |
                  I  |    | | R     |  \______| AN0        |
                     |    | |     __|  /      |            |
                           -     |  |/        |            |
                           |     |            |            |
                           |-----             |            |
                           |               ---|            |
                           |              |   |            |
                           |              |   |            |
                           |               -->| RX         |
                                              |            |
                                               ------------

The ISR will work like a debounce routine  and then outputs the value that
will be read by the UART (i think this is easier them doing that by
software).

This is part of my hack of a master M-Bus transceiver, the rest is still
growing in my mind. Any help... comments... ideas ?..

1997\05\16@141157 by Gerhard Fiedler

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At 12:20 16/05/97 +0000, Antonio Almeida wrote:
>The ISR will work like a debounce routine  and then outputs the value that
>will be read by the UART (i think this is easier them doing that by
>software).

I'd try to "debounce" the comparator output properly in hardware (right
switching point, right hysteresis), then you should be able to go directly
into the UART.

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