Motorola MC68HC05RC8 User Manual
Carrier Modulator Transmitter (CMT)
Modulator
MC68HC05RC16 — Rev. 3.0
General Release Specification
MOTOROLA
Carrier Modulator Transmitter (CMT)
77
Figure 9-8. CMT Operation in Time Mode
9.5.2 FSK Mode
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).
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 can automatically generate a phase-coherent,
dual-frequency FSK signal with programmable burst and interburst
gaps.
by the CPU, FSK mode can automatically generate a phase-coherent,
dual-frequency FSK signal with programmable burst and interburst
gaps.
MODULATOR GATE
f
OSC
÷
8
TIME MODE OUTPUT
BASEBAND OUTPUT
MARK
SPACE
MARK
MARK
SPACE
CARRIER FREQUENCY