668-0011 Rabbit Semiconductor, 668-0011 Datasheet - Page 179

• 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

20. I
C
NPUT
APTURE
20.1 Overview
The Input Capture peripheral consists of two channels, each of which contains a 16-bit
counter and edge-detection circuitry. The Input Capture channels are usually used to deter-
mine the time between events. An event is signaled by a rising or falling edge (or option-
ally by either edge) on one of 16 input pins that can be selected as the input for either of
the two channels. The Input Capture channels synchronize their inputs to the Input Capture
clock (from Timer A8), providing a low-pass filter functionality on the inputs, as shown in
Section 20.2.4.
When capturing an input, the channel starts/stops the counter (clocked by Timer A8)
according to the signal edges on various parallel port pins, providing the ability to measure
pulse widths and time intervals between external events, time-stamp signal changes on a
pin, and measure time intervals between a software start and an external event. An inter-
rupt can also be generated when an edge is detected.
A 16 bit counter is used to record the time at which the event takes place. The counter is
driven by the output of Timer A8 and can be set to count at a rate ranging from the full
clock speed (perclk/2) down to 1/256 the clock speed (perclk/512).
Two events are recognized: a start condition and a stop condition. The start condition may
be used to start counting and the stop condition to stop counting. However, the counter may
also run continuously or run until a stop condition is encountered. The start and stop condi-
tions may also be used to latch the current count at the instant the condition occurs rather
than actually start or stop the counter. The same pin may be used to detect the start and
stop condition—for example a rising edge could be the start condition and a falling edge
could be the stop condition. The start and stop condition can also be input on separate pins.
The Input Capture channels can be used to measure the width of fast pulses. This is done
by starting the counter on the first edge of the pulse and capturing the counter value on the
second edge of the pulse. In this case the maximum error in the measurement is approxi-
mately 2 periods of the clock used to count the counter. If there is sufficient time between
events for an interrupt to take place the unit can be set up to capture the counter value on
either start or stop conditions (or both) and cause an interrupt each time the count is cap-
tured. The counter can also be cleared and started under software control and then have its
value captured in response to an input.
The capture counter can be synchronized with Timer B outputs to load parallel port output
registers. This makes it possible to generate an output signal precisely synchronized with
Chapter 20 Input Capture
169