Carrier Modulator Transmitter (CMT)

Modulator

fOSC ÷ 8

CARRIER FREQUENCY

MODULATOR GATE

MARK

SPACE

MARK

SPACE

MARK

TIME MODE OUTPUT

BASEBAND OUTPUT

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).

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.

MC68HC05RC16 — Rev. 3.0

 

General Release Specification

 

 

 

MOTOROLA

Carrier Modulator Transmitter (CMT)

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