K60P100M100SF2RM Datasheet, PDF (1103/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Chapter 42 Carrier Modulator Transmitter (CMT)
The activation of modulation space period is done when the carrier signal is low to
prohibit cutting off the high pulse of a carrier signal. If the carrier signal is high, the
modulator extends the mark period until the carrier signal become low. To de-assert the
space period and assert the mark period, the carrier signal must have gone low to assure
that a space period is not erroneously shortened.
Should the contents of the modulation space period register be all zeroes, the match will
be immediate and no space period will be generated (for instance, for FSK protocols that
require successive bursts of different frequencies).
MSC[MCGEN] must be set to enable the modulator timer.
16 B ITS
0
CMTCMD1:CMTCMD2
MODE
17-BIT DOWN COUNTER *
16
=?
16
LOAD
CLOCK CONTROL
8
CMTCLOCK
CARRIER OUT (fcg)
MODULATOR GATE
SYSTEM CONTROL
MODULATOR
OUT
EOC FLAG SET
MODULE INTERRUPT REQUEST
PR IM AR Y/SEC O N D AR Y SELEC T
SPACE PERIOD REGISTER *
CMTCMD3:CMTCMD4
16 B ITS
* DENOTES HIDDEN REGISTER
Figure 42-16. Modulator Block Diagram
42.7.3.1 Time Mode
When the modulator operates in time mode (MSC[MCGEN] bit is set, MSC[BASE] and
MSC[FSK] bits are cleared), the modulation mark period consists of an integer number of
CMTCLK ÷ 8 clock periods. The modulation space period consists of zero or an integer
number of CMTCLK ÷ 8 clock periods. With an 8 MHz IF and MSC[CMTDIV] = 00,
the modulator resolution is 1 μs and has a maximum mark and space period of about
65.535 ms each . See the following figure for an example of the time mode and baseband
mode outputs.
The mark and space time equations for time and baseband mode are:
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.
1103