MC908KX2MDWE Datasheet, PDF (113/210 Pages) Freescale Semiconductor, Inc – High-performance M68HC08 architecture, Fully upward-compatible object code with M6805, M146805, and M68HC05 Families

Pin Name Conventions
12.3 Pin Name Conventions
The generic names of the SCI input/output (I/O) pins are:
• RxD, receive data
• TxD, transmit data
SCI I/O lines are implemented by sharing parallel I/O port pins. The full name of an SCI input or output
reflects the name of the shared port pin. Table 12-1 shows the full names and the generic names of the
SCI I/O pins.The generic pin names appear in the text of this section.
Table 12-1. Pin Name Conventions
Generic Pin
Names
Full Pin Names
RxD
PTB4/RxD
TxD
PTB5/TxD
12.4 Functional Description
Figure 12-3 shows the structure of the SCI module. The SCI allows full-duplex, asynchronous, NRZ serial
communication between the MCU and remote devices, including other MCUs. The transmitter and
receiver of the SCI operate independently, although they use the same baud rate generator.
The source of the baud rate clock is determined by the configuration register 2 bit, SCIBDSRC. If
SCIBDSRC is set then the source of the SCI is the internal data bus clock. If SCIBDSRC is cleared, the
source of the SCI is oscillator output CGMXCLK.
During normal operation, the CPU monitors the status of the SCI, writes the data to be transmitted, and
processes received data.
12.4.1 Data Format
The SCI uses the standard non-return-to-zero mark/space data format illustrated in Figure 12-2.
8-BIT DATA FORMAT
PARITY
BIT M IN SCC1 CLEAR
OR DATA
BIT
NEXT
START
START
BIT BIT 0 BIT 1 BIT 2 BIT 3 BIT 4 BIT 5 BIT 6 BIT 7 STOP BIT
BIT
START
9-BIT DATA FORMAT
BIT M IN SCC1 SET
PARITY
OR DATA
BIT
NEXT
START
BIT BIT 0 BIT 1 BIT 2 BIT 3 BIT 4 BIT 5 BIT 6 BIT 7 BIT 8 STOP BIT
BIT
Figure 12-2. SCI Data Formats
MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 Data Sheet, Rev. 2.1
Freescale Semiconductor
113