PIC16F1847_13 Datasheet, PDF (194/440 Pages) Microchip Technology – 18/20/28-Pin Flash Microcontrollers with XLP Technology

PIC16(L)F1847
23.1 DSM Operation
The DSM module can be enabled by setting the MDEN
bit in the MDCON register. Clearing the MDEN bit in the
MDCON register, disables the DSM module by
automatically switching the carrier high and carrier low
signals to the VSS signal source. The modulator signal
source is also switched to the MDBIT in the MDCON
register. This not only assures that the DSM module is
inactive, but that it is also consuming the least amount
of current.
The values used to select the carrier high, carrier low,
and modulator sources held by the Modulation Source,
Modulation High Carrier, and Modulation Low Carrier
control registers are not affected when the MDEN bit is
cleared and the DSM module is disabled. The values
inside these registers remain unchanged while the
DSM is inactive. The sources for the carrier high,
carrier low and modulator signals will once again be
selected when the MDEN bit is set and the DSM
module is again enabled and active.
The modulated output signal can be disabled without
shutting down the DSM module. The DSM module will
remain active and continue to mix signals, but the
output value will not be sent to the MDOUT pin. During
the time that the output is disabled, the MDOUT pin will
remain low. The modulated output can be disabled by
clearing the MDOE bit in the MDCON register.
23.2 Modulator Signal Sources
The modulator signal can be supplied from the follow-
ing sources:
• CCP1 Signal
• CCP2 Signal
• CCP3 Signal
• CCP4 Signal
• MSSP1 SDO1 Signal (SPI Mode Only)
• MSSP2 SDO2 Signal (SPI Mode Only)
• Comparator C1 Signal
• Comparator C2 Signal
• EUSART TX Signal
• External Signal on MDMIN1 pin
• MDBIT bit in the MDCON register
The modulator signal is selected by configuring the
MDMS <3:0> bits in the MDSRC register.
23.3 Carrier Signal Sources
The carrier high signal and carrier low signal can be
supplied from the following sources:
• CCP1 Signal
• CCP2 Signal
• CCP3 Signal
• CCP4 Signal
• Reference Clock Module Signal
• External Signal on MDCIN1 pin
• External Signal on MDCIN2 pin
• VSS
The carrier high signal is selected by configuring the
MDCH <3:0> bits in the MDCARH register. The carrier
low signal is selected by configuring the MDCL <3:0>
bits in the MDCARL register.
23.4 Carrier Synchronization
During the time when the DSM switches between
carrier high and carrier low signal sources, the carrier
data in the modulated output signal can become
truncated. To prevent this, the carrier signal can be
synchronized to the modulator signal. When synchroni-
zation is enabled, the carrier pulse that is being mixed
at the time of the transition is allowed to transition low
before the DSM switches over to the next carrier
source.
Synchronization is enabled separately for the carrier
high and carrier low signal sources. Synchronization for
the carrier high signal can be enabled by setting the
MDCHSYNC bit in the MDCARH register. Synchroniza-
tion for the carrier low signal can be enabled by setting
the MDCLSYNC bit in the MDCARL register.
Figure 23-1 through Figure 23-5 show timing diagrams
of using various synchronization methods.
DS40001453D-page 194
Preliminary
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