Freescale Semiconductor PXR4030, Reference Manual

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Enhanced Modular Input/Output Subsystem (eMIOS200)
23-62 Freescale Semiconductor
PXR40 Microcontroller Reference Manual, Rev. 1
23.4.1.2 Input Programmable Filter (IPF)
The IPF is a 5-bit programmable up counter that is incremented by the selected clock source, according to
IF bits in EMIOS_CCR[
n ]. The IPF ensures that only valid input pin transitions are received by the unified
channel edge detector. Figure 23-57 shows a block diagram of the IPF.
Figure 23-57. lnput Programmable Filter Submodule Diagram
The input signal is synchronized by system clock. When a state change occurs in this signal, the 5-bit
counter starts counting up. As long as the new state is stable on the pin, the counter remains incrementing.
If a counter overflow occurs, the new pin value is validated. In this case, it is transmitted as a pulse edge
to the edge detector. If the opposite edge appears on the pin before validation (overflow), the counter is
reset. At the next pin transition, the counter starts counting again. Any pulse that is shorter than a full range
of the masked counter is regarded as a glitch and it is not passed on to the edge detector.
Figure 23-58
shows a timing diagram of the input filter.
Figure 23-58. Input Programmable Filter Example
The filter is not disabled during either freeze state or negated GTBE input.
23.4.1.3 Clock Prescaler (CP)
The CP divides the GCP output signal to generate a clock enable for the internal counter of the unified
channels. It is a programmable 2-bit down counter. The GCP output signal is prescaled by the value
defined in the UCPRE bits in the EMIOS_CCR[
n ] register. The output is clocked every time the counter
reaches zero. Counting is enabled by setting the UCPREN bit in the EMIOS_CCR[ n ]. The counter can be
stopped at any time by clearing this bit, thereby stopping the internal counter in the unified channel.
Synchronizer
IF3
clk
IF2 IF1 IF0
5-bit Up Counter
FCK
Prescaled Clock
EMIOSI
Clock
System Clock
Filter Out
Selected Clock
5-bit Counter
Filter Out
EMIOSI
Time
IF[3:0] = 0010