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Rabbit 6000 User’s Manual
digi.com
333
29. Q
UADRATURE
D
ECODER
29.1 Overview
The Rabbit 6000 has a two-channel Quadrature Decoder that accepts inputs via specific pins on Parallel
Ports D and E. Each channel has two inputs, the in-phase (I) input and the 90 degree or quadrature-phase
(Q) input. An 8 or 10-bit up/down counter counts encoder steps in the forward and backward directions,
and provides interrupts when the count goes from 0x00 to 0xFF (or 0x3FF) or from 0xFF (or 0x3FF) to
0x00. An interrupt can occur each time the count overflows or underflows. The Quadrature Decoder con-
tains digital filters on the inputs to prevent false counts.
The external signals are synchronized with an internal clock provided by the output of Timer A10.
Each Quadrature Decoder channel accepts inputs from either the upper nibble or lower nibble of Parallel
Ports D and E. The I signal is input on an odd-numbered port bit, while the Q signal is input on an even-
numbered port bit. There is also a disable selection, which is guaranteed to not generate a count increment
or decrement on either entering or exiting the disabled state.
The operation of the counter as a function of the I and Q inputs is shown below.
Summary of Contents for 6000
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