HC705RC16GRSSLASHD datasheet(66/120 Pages) NXP

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Carrier Modulator Transmitter (CMT)

General Release Specification

MC68HC705RC16 — Rev. 3.0

Carrier Modulator Transmitter (CMT)

used to change the state of the infrared out pin (IRO) directly. This

feature allows for the generation of future protocols not readily

producible by the current architecture.

9.3 Overview

The module consists of carrier generator, modulator, and transmitter

output blocks. The block diagram is shown in Figure 9-1.

The carrier generator has a resolution of 500 ns with a 2-MHz oscillator.

The user may independently define the high and low times of the carrier

signal to determine both period and duty cycle. The carrier generator can

generate signals with periods between 1

µs (1 MHz) and 64 µs (15.6

kHz) in steps of 500 ns. The possible duty cycle options will depend

upon the number of counts required to complete the carrier period. For

example, a 400-kHz signal has a period of 2.5

µs and will therefore

require 5 x 500 ns counts to generate. These counts may be split

between high and low times so the duty cycles available will be 20% (one

high, four low), 40% (two high, three low), 60% (three high, two low) and

80% (four high, one low). For lower frequency signals with larger

periods, higher resolution (as a percentage of the total period) duty

cycles are possible. The carrier generator may select between two sets

of high and low times. When operating in normal mode (subsequently

referred to as time mode), just one set will be used. When operating in

FSK (frequency shift key) mode, the generator will toggle between the

two sets when instructed to do so by the modulator, allowing the user to

dynamically switch between two carrier frequencies without CPU

intervention. When the BASE bit in the modulator control and status

continuously to allow for the generation of baseband protocols. See 9.4

Carrier Generator.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

HC705RC16GRS/D Datasheet(PDF) 66 Page - NXP Semiconductors