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Serial Communications Interface (SCI)

Pin Name Conventions

MC68HC908GR8 — Rev 4.0

Technical Data

MOTOROLA

Serial Communications Interface (SCI)

233

18.4 Pin Name Conventions

The generic names of the SCI I/O pins are:

•

RxD (receive data)

•

TxD (transmit data)

SCI I/O (input/output) 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 18-1 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.

18.5 Functional Description

Figure 18-1 shows the structure of the SCI module. The SCI allows full-

duplex, asynchronous, NRZ serial communication among 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. During normal operation, the CPU monitors the status of the

SCI, writes the data to be transmitted, and processes received data.

The baud rate clock source for the SCI can be selected via the

configuration bit, SCIBDSRC, of the CONFIG2 register ($001E). Source

selection values are shown in Figure 18-1.

Table 18-1. Pin Name Conventions

Generic Pin Names:

RxD

TxD

Full Pin Names:

PE1/RxD

PE0/TxD

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