CMPx_MUXCR field descriptions (continued)
Field
Description
110
IN6
111
IN7
26.8 Functional description
The CMP module can be used to compare two analog input voltages applied to INP and
INM. CMPO is high when the non-inverting input is greater than the inverting input, and
is low when the non-inverting input is less than the inverting input. This signal can be
selectively inverted by setting CR1[INV] = 1.
SCR[IER] and SCR[IEF] are used to select the condition which will cause the CMP
module to assert an interrupt to the processor. SCR[CFF] is set on a falling-edge and
SCR[CFR] is set on rising-edge of the comparator output. The optionally filtered CMPO
can be read directly through SCR[COUT].
26.8.1 CMP functional modes
There are three main sub-blocks to the CMP module:
• The comparator itself
• The window function
• The filter function
The filter, CR0[FILTER_CNT], can be clocked from an internal or external clock source.
The filter is programmable with respect to the number of samples that must agree before
a change in the output is registered. In the simplest case, only one sample must agree. In
this case, the filter acts as a simple sampler.
The external sample input is enabled using CR1[SE]. When set, the output of the
comparator is sampled only on rising edges of the sample input.
The "windowing mode" is enabled by setting CR1[WE]. When set, the comparator output
is sampled only when WINDOW=1. This feature can be used to ignore the comparator
output during time periods in which the input voltages are not valid. This is especially
useful when implementing zero-crossing-detection for certain PWM applications.
The comparator filter and sampling features can be combined as shown in the following
table. Individual modes are discussed below.
Chapter 26 Comparator (CMP)
KL02 Sub-Family Reference Manual, Rev. 2.1, July 2013
Freescale Semiconductor, Inc.
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