
Infrared Functional Description
MC68HC08LK60 MC68HC908LK60 Advance Information Data Sheet, Rev. 1.1
Freescale Semiconductor
121
12.4 Infrared Functional Description
The infrared submodule consists of two major blocks: a transmit encoder and a receive decoder as shown
Figure 12-2. Infrared Submodule Diagram
This module provides the capability of transmitting narrow pulses to the IR LED and receiving narrow
pulses and transforming them to serial bits, which are sent to the SCI. The infrared submodule receives
its clock sources from the SCI. One of these two clocks are selected in the infrared submodule to generate
either 3/16, 1/16, or 1/32 narrow pulses during transmission.
12.4.1 Infrared Transmit Encoder
The infrared transmit block converts serial bits of data from the SCI module to narrow low pulses (pin TxD)
when a zero bit in the serial stream is received. The narrow pulse is sent in the middle of the bit with a
duration of 1/32, 1/16, or 3/16 of a bit time. When two 0s are sent, the first narrow pulse is sent in the
middle of the bit, and then after one bit time, another narrow pulse is sent in the middle of the second bit.
12.4.2 Infrared Receive Decoder
The infrared receive block converts low narrow pulses from pin RxD to standard SCI data bits using the
SCI_R16XCK clock. This signal clocks a 4-bit internal counter which ranges from 0 to 15. The incoming
pulse enables the internal counter and a 0 is sent out to the Ir_RXD output. If a second pulse or several
pulses occur between count 0 and 7, these pulses are ignored. When the counter is greater than 7, and
if another pulse occurs, the counter is reset and the Ir_RXD output remains 0. After the counter reaches
15, the Ir_RXD output returns to 1. The circuit then waits for another input pulse and the process is
repeated. If a pulse arrives shortly after the counter reaches 15 due to jitter, the Ir_RXD output remains
1 until the pulse occurs. Then a 0 is sent out to Ir_RXD.
RxD
TxD
RxD
TRANSMIT
IR_TxD
RxD
SCI_R16XCLK
SCI_R32XCLK
TNP[1:0]
MUX
TxD
ENCODER
IREN
RECEIVE
DECODER
IREN
MUX
IR_RxD