MC9S08RC8 Datasheet, PDF (108/234 Pages) Freescale Semiconductor, Inc – Microcontrollers

Carrier Modulator Transmitter (CMT) Block Description
8.2 Features
The CMT consists of a carrier generator, modulator, and transmitter that drives the infrared out (IRO) pin.
The features of this module include:
• Four modes of operation
— Time with independent control of high and low times
— Baseband
— Frequency shift key (FSK)
— Direct software control of IRO pin
• Extended space operation in time, baseband, and FSK modes
• Selectable input clock divide: 1, 2, 4, or 8
• Interrupt on end of cycle
— Ability to disable IRO pin and use as timer interrupt
8.3 CMT Block Diagram
PRIMARY/SECONDARY SELECT
MODULATOR
CLOCK
CONTROL
CMTCLK
CARRIER
GENERATOR
CARRIER
OUT (f_CG)
MODULATOR
OUT
TRANSMITTER
OUTPUT
IRO
PIN
CMTDIV
CMT REGISTERS
AND BUS INTERFACE
BUS CLOCK
INTERNAL BUS
IIREQ
Figure 8-2. Carrier Modulator Transmitter Module Block Diagram
8.4 Pin Description
The IRO pin is the only pin associated with the CMT. The pin is driven by the transmitter output when the
MCGEN bit in the CMTMSC register and the IROPEN bit in the CMTOC register are set. If the MCGEN
bit is clear and the IROPEN bit is set, the pin is driven by the IROL bit in the CMTOC register. This enables
user software to directly control the state of the IRO pin by writing to the IROL bit. If the IROPEN bit is
clear, the pin is disabled and is not driven by the CMT module. This is so the CMT can be configured as a
modulo timer for generating periodic interrupts without causing pin activity.
MC9S08RC/RD/RE/RG Data Sheet, Rev. 1.11
108
Freescale Semiconductor