MC68340 datasheet(303/441 Pages) FREESCALE

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MC68340 USER’S MANUAL

MOTOROLA

7.3 OPERATION

The following paragraphs describe the operation of the baud rate generator, transmitter

and receiver, and other functional operating modes of the serial module.

7.3.1 Baud Rate Generator

The baud rate generator consists of a crystal oscillator, baud rate generator, and clock

selectors (see Figure 7-3). The crystal oscillator operates directly from a 3.6864-MHz

crystal or from an external clock of the same frequency. The SCLK input bypasses the

baud rate generator and provides a synchronous clock mode of operation when used as a

divide-by-1 clock and an asynchronous clock mode when used as a divide-by-16 clock.

The clock is selected by programming the clock-select register (CSR) for each channel.

.. .

. ......

BAUD RATE

GENERATOR LOGIC

CRYSTAL

OSCILLATOR

BAUD RATE

GENERATOR

CLOCK

SELECTORS

SCLK

EXTERNAL

INTERFACE

Figure 7-3. Baud Rate Generator Block Diagram

7.3.2 Transmitter and Receiver Operating Modes

The functional block diagram of the transmitter and receiver, including command and

operating registers, is shown in Figure 7-4. The paragraphs that follow contain

descriptions for both these functions in reference to this diagram. For detailed register

information, refer to 7.4 Register Description and Programming.

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