Datasheet

 2012 Microchip Technology Inc. DS30684A-page 325
PIC18(L)F2X/45K50
20.1.4 EDGE STATUS
The CTMUCONL register also contains two status bits:
EDG2STAT and EDG1STAT (CTMUCONL<1:0>).
Their primary function is to show if an edge response
has occurred on the corresponding channel. The
CTMU automatically sets a particular bit when an edge
response is detected on its channel. The level-sensitive
nature of the input channels also means that the status
bits become set immediately if the channel’s configura-
tion is changed and is the same as the channel’s
current state.
The module uses the edge status bits to control the cur-
rent source output to external analog modules (such as
the A/D Converter). Current is only supplied to external
modules when only one (but not both) of the status bits
is set, and shuts current off when both bits are either
set or cleared. This allows the CTMU to measure cur-
rent only during the interval between edges. After both
status bits are set, it is necessary to clear them before
another measurement is taken. Both bits should be
cleared simultaneously, if possible, to avoid re-enabling
the CTMU current source.
In addition to being set by the CTMU hardware, the
edge status bits can also be set by software. This is
also the user’s application to manually enable or
disable the current source. Setting either one (but not
both) of the bits enables the current source. Setting or
clearing both bits at once disables the source.
20.1.5 INTERRUPTS
The CTMU sets its interrupt flag (PIR3<3>) whenever
the current source is enabled, then disabled. An
interrupt is generated only if the corresponding
interrupt enable bit (PIE3<3>) is also set. If edge
sequencing is not enabled (i.e., Edge 1 must occur
before Edge 2), it is necessary to monitor the edge
Status bits and determine which edge occurred last and
caused the interrupt.
20.2 CTMU Module Initialization
The following sequence is a general guideline used to
initialize the CTMU module:
1. Select the current source range using the IRNG
bits (CTMUICON<1:0>).
2. Adjust the current source trim using the ITRIM
bits (CTMUICON<7:2>).
3. Configure the edge input sources for Edge 1 and
Edge 2 by setting the EDG1SEL and EDG2SEL
bits (CTMUCONL<3:2 and 6:5>).
4. Configure the input polarities for the edge inputs
using the EDG1POL and EDG2POL bits
(CTMUCONL<4,7>). The default configuration
is for negative edge polarity (high-to-low
transitions).
5. Enable edge sequencing using the EDGSEQEN
bit (CTMUCONH<2>). By default, edge
sequencing is disabled.
6. Select the operating mode (Measurement or
Time Delay) with the TGEN bit. The default
mode is Time/Capacitance Measurement.
7. Discharge the connected circuit by setting the
IDISSEN bit (CTMUCONH<1>); after waiting a
sufficient time for the circuit to discharge, clear
IDISSEN.
8. Disable the module by clearing the CTMUEN bit
(CTMUCONH<7>).
9. Enable the module by setting the CTMUEN bit.
10. Clear the Edge Status bits: EDG2STAT and
EDG1STAT (CTMUCONL<1:0>).
11. Enable both edge inputs by setting the EDGEN
bit (CTMUCONH<3>).
Depending on the type of measurement or pulse
generation being performed, one or more additional
modules may also need to be initialized and configured
with the CTMU module:
• Edge Source Generation: In addition to the
external edge input pins, both Timer1 and the
Output Compare/PWM1 module can be used as
edge sources for the CTMU.
• Capacitance or Time Measurement: The CTMU
module uses the A/D Converter to measure the
voltage across a capacitor that is connected to one
of the analog input channels.
• Pulse Generation: When generating system clock
independent output pulses, the CTMU module
uses Comparator 2 and the associated
comparator voltage reference.