MC68HC05RC17 Datasheet, PDF (79/128 Pages) Freescale Semiconductor, Inc – General Release Specification

9.5.2 FSK Mode
Freescale Semiconductor, Inc.
Carrier Modulator Transmitter (CMT)
Modulator
When the modulator operates in FSK mode, 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); however, in FSK mode the
carrier switches between data registers in preparation for the next mark
period. The carrier generator toggles between primary and secondary
data register values whenever the modulator mark period expires. The
space period provides an interpulse gap (no carrier), but if SBUFF = 0,
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 automatically can generate a phase-coherent,
dual-frequency FSK signal with programmable burst and interburst
gaps.
The mark and space time equations for FSK mode are:
tmark = ^{M------B----U--f--c-F--g--F-----+-----1--sec} s
tspace = ^{S-----B--f--cU---g--F----F--} sec s
Where f_cg is the frequency output from the carrier generator, setting the
DIV2 bit in the MCSR will double mark and space times.
MC68HC05RC17 — Rev. 2.0
General Release Specification
Carrier Modulator Transmitter (CMT)
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