Rabbit 6000 User’s Manual
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337
29.3 Operation
The following steps explain how to set up a Quadrature Decoder channel.
1. Configure Timer A10 via TAT10R to provide the desired Quadrature Decoder clock speed (and
optionally TA12R).
2. Configure QDCR to select the input pins for the two channels.
3. Reset the counters by writing to QDCSR.
29.3.1 Handling Interrupts
The following steps explain how an interrupt is set up and used.
1. Write the vector to the interrupt service routine to the internal interrupt table.
2. Configure QDCR to select the interrupt priority (note that interrupts will be enabled once this value
is set).
The following actions occur within the interrupt service routine.
•
Determine exactly why the interrupt occurred by reading the status bits in QDCSR; if the interrupt
occurred due to a counter rollover, adjust any software counters accordingly. Reading QDCSR will also
clear the interrupt request.
•
The current counter value can be read from QDCxR (and QDCxHR if the 10-bit counter is enabled).
29.3.2 Example ISR
A sample interrupt handler is shown below.
qd_isr::
push af ; save used registers
ioi ld a, (QDCSR) ; clear the interrupt request and get status
; perform any necessary software counter adjustments here
; read current counter value(s)
pop af ; restore used registers
ipres
ret
Summary of Contents for 6000
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