668-0011 Rabbit Semiconductor, 668-0011 Datasheet - Page 188

• Manufacturer Part Number: 668-0011
• Description: IC MPU RABIT3000A 55.5MHZ128LQFP
• Manufacturer: Rabbit Semiconductor

Specifications of 668-0011

• 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: 316-1043

The Quadrature Decoders are clocked by the output of Timer A10, giving a maximum
clock rate from perclk/2 down to perclk/512. The time constant of Timer A10 must be fast
enough to sample the inputs properly. Both the I and Q inputs go through a digital filter
that rejects pulses shorter than two clock period wide. In addition, the clock rate must be
high enough that transitions on the I and Q inputs are sampled in different clock cycles.
Input capture may be used to measure the pulse width on the I inputs because they come
from the odd-numbered port bits. The operation of the digital filter is shown below.
The Quadrature Decoder generates an interrupt when the counter increments from 0xFF
(0x3FF in 10-bit mode) to 0x00, or when the counter decrements from 0x00 to 0xFF
(0x3FF in 10-bit mode). The timing for the interrupt is shown below. Note that the status
bits in the QDCSR are set coincident with the interrupt, and the interrupt and status bits
are cleared by reading the QDCSR.
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Rabbit 3000 Microprocessor User’s Manual