mcf51jf128 Freescale Semiconductor, Inc, mcf51jf128 Datasheet - Page 787

• Manufacturer Part Number: mcf51jf128
• Description: Mcf51jf128 Reference Manual
• Manufacturer: Freescale Semiconductor, Inc

Assuming that the high time count compare register is currently active, a valid compare
will cause the carrier output to be driven low. The counter will continue to increment
(starting at reset value of 0x01). When the value stored in the selected low count value
register is reached, the counter will again be reset and the carrier output will be driven
high.
The cycle repeats, automatically generating a periodic signal which is directed to the
modulator . The lowest frequency (maximum period) and highest frequency (minimum
period) which can be generated are defined as:
f
f
In the general case, the carrier generator output frequency is:
f
Where: 0 < Highcount < 256 and
The duty cycle of the carrier signal is controlled by varying the ratio of high time to low
+ high time. As the input clock period is fixed, the duty cycle resolution will be
proportional to the number of counts required to generate the desired carrier period.
36.7.3 Modulator
The modulator block controls the state of the infrared out signal (IRO) . The modulator
output is gated on to the IRO signal when the modulator/carrier generator is enabled .
When the modulator/carrier generator is disabled, the IRO signal is controlled by the state
of the IRO latch. OC[CMTPOL] enables the IRO signal to be active high or active low.
In CMT modes, the modulator functions as givenbelow:
Freescale Semiconductor, Inc.
max
min
cg
• In Time mode, the modulator can gate the carrier onto the modulator output.
• In Baseband mode, the modulator can control the logic level of the modulator output.
• In FSK mode, the modulator can count carrier periods and instruct the carrier
= f
= f
0 < Lowcount < 256
generator to alternate between two carrier frequencies whenever a modulation period
(mark + space counts) expires.
= f
CMTCLK
CMTCLK
CMTCLK
÷ (Highcount + Lowcount) Hz
÷ (2 x (2
÷ (2 x 1) Hz
8
MCF51JF128 Reference Manual, Rev. 2, 03/2011
− 1)) Hz
Preliminary
Chapter 36 Carrier Modulator Transmitter (CMT)
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