SPMCK16Z4MPV20 datasheet(257/500 Pages) FREESCALE

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M68HC16 Z SERIES

MULTICHANNEL COMMUNICATION INTERFACE

USER’S MANUAL

10-17

10.4.3 Receive Data Pins (RXDA, RXDB)

RXDA and RXDB are the serial data inputs to the SCIA and SCIB interfaces, respec-

tively. Each pin is also available as a general-purpose I/O pin when the RE bit in

SCCR1 of the associated SCI submodule is cleared. When used for general-purpose

I/O, RXDA and RXDB may be configured either as input or output as determined by

the RXDA and RXDB bits in the MDDR.

10.4.4 Transmit Data Pins (TXDA, TXDB)

When used for general-purpose I/O, TXDA and TXDB can be configured either as in-

put or output as determined by the TXDA and TXDB bits in the MDDR. The TXDA and

TXDB pins are enabled for SCI use by setting the TE bit in SCCR1 of each SCI inter-

face.

10.4.5 SCI Operation

SCI operation can be polled by means of status flags in the SCSR, or interrupt-driven

operation can be employed by means of the interrupt-enable bits in SCCR1.

10.4.5.1 Definition of Terms

Data can be transmitted and received in a number of formats. The following terms con-

cerning data format are used in this section:

• Bit-Time — The time required to transmit or receive one bit of data, which is equal

to one cycle of the baud frequency.

• Start Bit — One bit-time of logic zero that indicates the beginning of a data frame.

A start bit must begin with a one-to-zero transition and be preceded by at least

three receive time samples of logic one.

• Stop Bit — One bit-time of logic one that indicates the end of a data frame.

• Frame — A complete unit of serial information. The SCI can use 10-bit or 11-bit

frames.

• Data Frame — A start bit, a specified number of data or information bits, and at

least one stop bit.

• Idle Frame — A frame that consists of consecutive ones. An idle frame has no

start bit.

• Break Frame — A frame that consists of consecutive zeros. A break frame has

no stop bits.

Table 10-5 SCI Pins

Mode

SCI Function

Port I/O Signal

Transmit data

TXDA

Serial data output from SCIA (TE = 1)

PMC7

TXDB

Serial data output from SCIB (TE = 1)

PMC5

Receive data

RXDA

Serial data input to SCIA (RE = 1)

PMC6

RXDB

Serial data input to SCIB (RE = 1)

PMC4

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