Freescale Semiconductor, Inc.
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
EXTERNAL
ERFACE
I
...
N
.
..... .... .
T
X1
BAUD RATE
X2
GENERATOR
SCLK
CLOCK
SELECTORS
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.
7- 8
MC68340 USER’S MANUAL
MOTOROLA
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