In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Zoot wrote:

That's fine if that's all that's going to happen -- in my own projects I always use (or like to leave open) the ability to have real-time or other RTC processes (i.e. ms or us counters in the ISR, serial comms w/buffer, PWM, IR generation, IR communication tx/rx, etc.).

If the commitment is made to pin generated interrupt *hardware* then it can be a one-way street. For example, in my code above, I presume that the sample time is constant -- i.e. it's counting samples received in fairly precise 10ms frames (although there's no flag for the mainline). So if sample windows were an issue, a pure RTCC interrupt would prevent that.

Another way to put it -- with a few changes to bit frame counts, Jon's ISR based serial TX/RX w/buffers could be dropped right in w/o changes to firmware nor hardware.

David -- here's a slightly revised version that sets a flag to let the mainline know that the count has been "captured". The scenario below presumes that the mainline will never take more than 10ms before getting around to checking/clearing the flag (to keep this example relatively simple):

samplePin PIN RB.0 INPUT
Led PIN RB.1 OUTPUT

flag VAR Byte ' global var
sampleReady VAR flag.0

sampleFrame VAR Word
sampleCount VAR Word
sampleCaptured VAR Word
sampleState VAR Byte

__IsrRate    CON 400_000 '  will count pulses up to 100khz reliably
SampleHz   CON 100 ' this many samples per second

SampleTicksPerFrame  CON __IsrRate / SampleHz 

INTERRUPT __IsrRate

   sampleState.0 = samplePin ' capture pin right now
   IF sampleState.0 = 1 THEN ' this state was 1
         IF sampleState.1 = 0 THEN ' previous state 0, must be rising edge
             INC sampleCount
         ENDIF
   ENDIF
   sampleState = sampleState << 1 ' save current state as previous

   INC sampleFrame
   IF sampleFrame >= MySampleRate THEN ' capture
       sampleCaptured = sampleCount
       sampleCount = 0
       sampleFrame = 0
       sampleReady = 1 ' set flag for mainline
       Led = ~Led ' toggle led -- this would be 50% duty cycle at the sample rate (in this case 100hz)
   ENDIF

   RETURNINT

Start:


Main:

   IF sampleReady = 1 THEN ' must have captured a value during a 10ms sample frame
        ' debug or display or watch the value: sampleCaptured
        sampleReady = 0 ' clear the flag
   ENDIF

   GOTO Main

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