Rabbit 6000 User’s Manual
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29.2 Dependencies
29.2.1 I/O Pins
Each Quadrature Decoder channel can accept the two encoder inputs from one of three different locations,
as shown in the table below. Each channel can select a different input option. Note that these pins can be
used for other peripherals at the same time as the Quadrature Decoder peripheral; one example of this use
is to measure pulse width on the I channels with the input capture peripheral.
29.2.2 Clocks
The 8/10-bit Quadrature Decoder counters are clocked from the output of Timer A10, and can run at rates
from the peripheral clock divided by 2 down to the peripheral clock divided by 512 by writing the appro-
priate value to TAT10R. Timer A12 can be used as a predivider for Timer A10.
Both the I and Q inputs go through a digital filter that rejects pulses shorter than two clock periods wide.
29.2.3 Other Registers
29.2.4 Interrupts
Each Quadrature Decoder channel can generate an interrupt whenever the counter increments from 0x0FF
(0x3FF in 10-bit mode) to 0x00 or when the counter decrements from 0x000 to 0x0FF (0x3FF for 10-bit
mode). The interrupt request is cleared when QDCSR is read.
The Quadrature Decoder interrupt vector is in the IIR at offset 0x190. It can be set as Priority 1, 2, or 3.
The status bits in the QDCSR are set coincident with the interrupt request and are reset when QDCSR is
read.
Inputs
Channel 1
Channel 2
I
Q
I
Q
Option 1
PD1
PD0
PD3
PD2
Option 2
PE1
PE0
PE3
PE2
Option 3
PE5
PE4
PE7
PE6
Register
Function
TAT10R
Time constant for Quadrature Decoder clock
TAT12R
Optional predivider for Timers A8-11.
TAECR
Enable for Timer A12 prescaling.
Summary of Contents for 6000
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