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 register (MCSR) is set, the carrier output to the modulator is held high continuously to allow for the generation of baseband protocols. See 9.4 Carrier Generator.
General Release Specification | | MC68HC05RC16 — Rev. 3.0 |
| | |
68 | Carrier Modulator Transmitter (CMT) | MOTOROLA |
