MC68HC908LJ12 Datasheet, PDF (231/413 Pages) Freescale Semiconductor, Inc – 8-bit microcontroller units

Infrared Serial Communications
The infrared sub-module receives two clock sources from the SCI
module: SCI_R16XCLK and SCI_R32XCLK. Both reference clocks are
used to generate the narrow pulses during data transmission.
The SCI_R16XCLK and SCI_R32XCLK are internal clocks with
frequencies that are 16 and 32 times the baud rate respectively. Both
SCI_R16XCLK and SCI_R32XCLK clocks are used for transmitting
data. The SCI_R16XCLK clock is used only for receiving data.
NOTE:
For proper SCI function (transmit or receive), the bus clock MUST be
programmed to at least 32 times that of the selected baud rate.
When the infrared sub-module is disabled, signals on the TxD and RxD
pins pass through unchanged to the SCI module.
13.6 Infrared Functional Description
Figure 13-3 shows the structure of the infrared sub-module.
TNP[1:0]
IREN
SCI_TxD
SCI_R32XCLK
SCI_R16XCLK
TRANSMIT
IR_TxD
ENCODER
MUX
TxD
IR_RxD
RECEIVE
DECODER
RxD
SCI_RxD
MUX
Technical Data
232
Figure 13-3. Infrared Sub-Module Diagram
The infrared sub-module provides the capability of transmitting narrow
pulses to an infrared LED and receiving narrow pulses and transforming
them to serial bits, which are sent to the SCI module. The infrared sub-
module receives two clocks from the SCI. One of these two clocks is
selected as the base clock to generate the 3/16, 1/16, or 1/32 bit width
narrow pulses during transmission.
MC68HC908LJ12 — Rev. 2.1
Infrared Serial Communications Interface Module (IRSCI) Freescale Semiconductor