>Robert Lunn wrote:
>>
>> >I need to measure a continuous frequency between 0 - 250 cycles/MINUTE,
>> >and transmit it via RS-232 at 2400 baud in a message containing 6 bytes
>> >once 5 seconds.
>>
>>         Peter, what's the six-byte message you send?
>>
>>         (I want to get a handle on the processing required to
>>          create the message string.)
>
>Bob,
>
>Sorry, but there are only five bytes and are as follows;
>
>Byte   Description
>-----------------------------------------------------------------
>  1    Start of Message ID    Constant
>  2-3  Unit Identification    15 bits constant (1 bit battery low)
>  4    Frequency Value        Variable
>  5    Checksum               Variable
>
>Sorry for the delay in answering, and thanks for your interest.
>
>Regards,
>
>Peter

Hmm. A six byte message at 1200 baud takes 0.05 seconds. At 250 rpm the
input pulses arrive every 0.3 seconds. So there's enough time between pulses
to send multiple messages if necessary.

Providing your transmit routine waits until just after a pulse (or counter
overflow when there's no input) it should have hardly any problems with
packets corrupted by interrupt servicing routines, in fact you should
probably disable the interrupt for 100mS after each pulse.

Disabling the interrupt allows for the situation where the flag is
stationary on the edges of the sensor and produces anomolously high
readings. These noise readings appear as 600 rpm and can be filtered out
(binned).

Just a few thoughts,

Keith.
==========================================================
Keith Dowsett         "Variables won't; constants aren't."

E-mail: kdowsett@rpms.ac.uk
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