mcf51jf128 Freescale Semiconductor, Inc, mcf51jf128 Datasheet - Page 791

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

36.7.3.3 FSK Mode
When the modulator operates in FSK mode (MSC[MCGEN] and MSC[FSK] bits are set,
and MSC[BASE] bit is cleared), the modulation mark and space periods consist of an
integer number of carrier clocks (space period can be zero). When the mark period
expires, the space period is transparently started (as in time mode). The carrier generator
toggles between primary and secondary data register values whenever the modulator
space period expires.
The space period provides an interpulse gap (no carrier). If CMD3:CMD4 = 0x0000, then
the modulator and carrier generator will switch between carrier frequencies without a gap
or any carrier glitches (zero space).
Using timing data for carrier burst and interpulse gap length calculated by the CPU, FSK
mode can automatically generate a phase-coherent, dual-frequency FSK signal with
programmable burst and interburst gaps.
The mark and space time equations for FSK mode are:
t
t
Where f
below shows what the IRO signal looks like in FSK mode with the following values:
CMD1:CMD2 = 0x0003, CMD3:CMD4 = 0x0002, primary carrier high count = 0x01,
primary carrier low count = 0x02, secondary carrier high count = 0x03, and secondary
carrier low count = 0x01.
Freescale Semiconductor, Inc.
mark
space
MODULATOR GATE
CARRIER OUT (f cg )
= (CMD1:CMD2 + 1) ÷ f
= CMD3:CMD4 ÷ f
cg
IR O SIGNAL
is the frequency output from the carrier generator. The example in figure
Figure 36-18. Example: CMT Output in FSK Mode
MARK1
MCF51JF128 Reference Manual, Rev. 2, 03/2011
cg
SPACE1
cg
MARK2
Preliminary
SPACE2
Chapter 36 Carrier Modulator Transmitter (CMT)
MARK1
SPACE1
MARK2
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