mpc823rg Freescale Semiconductor, Inc, mpc823rg Datasheet - Page 607

• Manufacturer Part Number: mpc823rg
• Description: Mpc823 Powerquicc Integrated Communications Processor For Portable Systems
• Manufacturer: Freescale Semiconductor, Inc

Freescale Semiconductor, Inc.
Communication Processor Module
The clock input to the prescaler can be selected by the EXTC field in the baud rate generator
configuration registers to originate in one of three sources—BRGCLK, CLK2 or CLK4.
The BRGCLK is generated in the MPC823 clock synthesizer specifically for the four baud
2
rate generators, serial peripheral interface, and I
C internal baud rate generator. You can
also configure the CLK2 or CLK4 pins to be the clock source. An external pin allows flexible
baud rate frequency generation, regardless of the system frequency. Additionally, the CLK2
or CLK4 pins allow a single external frequency to become the input clock for multiple baud
rate generators. The clock signals on the CLK2 or CLK4 pins are not synchronized internally
prior to being used by the baud rate generator.
Next, the baud rate generator provides a divide-by-16 option before the clock reaches the
prescaler. This option is chosen by the DIV16 bit. The clock is then divided into the prescaler
by a maximum of 4,096. This input clock divide ratio can be programmed on-the-fly.
However, on-the-fly baud rate generator changes must not occur within a shorter time than
the period of two baud rate generator input clocks.
Note: Four baud rate generators are available for the SCCs and SMCs. However,
BRGO3 and BRGO4 cannot be output externally.
The output of the prescaler is sent internally to the bank of clocks and can also be output
externally on the BRGOx pins of either the port A or port B parallel I/O. One BRGOx pin is
an output from the corresponding baud rate generator. If the baud rate generator divides the
clock by an even value, the transitions of the BRGOx pin always occur on the falling edge
of the input clock to the baud rate generator. If the baud rate generator is programmed to an
odd value, the transitions alternate between the falling and rising edges of the input clock.
Additionally, the output of the baud rate generator can be sent to the autobaud control block.
MPC823 REFERENCE MANUAL
16-155
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