668-0010 Rabbit Semiconductor, 668-0010 Datasheet - Page 187

• Manufacturer Part Number: 668-0010
• Description: IC MPU RABIT3000 55.5MHZ 128LQFP
• Manufacturer: Rabbit Semiconductor

Specifications of 668-0010

• Rohs Status: RoHS non-compliant
• Processor Type: Rabbit 3000 8-Bit
• Speed: 55.5MHz
• Voltage: 2.5V, 2.7V, 3V, 3.3V
• Mounting Type: Surface Mount
• Package / Case: 128-LQFP
• Features: -
• Other names: 316-1016

21. Q
D
UADRATURE
ECODER
21.1 Overview
The Rabbit 3000 has a two-channel Quadrature Decoder that accepts inputs via specific
pins on Parallel Port F. 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 from 0xFF to 0x00. An interrupt can occur each time the count over-
flows or underflows. The Quadrature Decoder contains digital filters on the inputs to pre-
vent 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 Port F. 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 not to 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.
Chapter 21 Quadrature Decoder
177