MPC8280 datasheet(633/1386 Pages) FREESCALE

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MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

17-1

Chapter 17

Baud-Rate Generators (BRGs)

The CPM contains eight independent, identical baud-rate generators (BRGs) that can be used with the

FCCs, SCCs, and SMCs. The clocks produced by the BRGs are sent to the bank-of-clocks selection logic,

where they can be routed to the controllers. In addition, the output of a BRG can be routed to a pin to be

used externally. The following is a list of BRGs’ main features:

•

Eight independent and identical BRGs

•

On-the-fly changes allowed

•

Each BRG can be routed to one or more FCCs, SCCs, or SMCs

•

A 16x divider option allows slow baud rates at high system frequencies

•

Each BRG contains an autobaud support option

•

Each BRG output can be routed to a pin (BRGOn)

Figure 17-1 shows a BRG.

Figure 17-1. Baud-Rate Generator (BRG) Block Diagram

Each BRG clock source can be BRGCLK, or a choice of two external clocks (selected in BRGCx[EXTC]).

The BRGCLK is an internal signal generated in the MPC8280 clock synthesizer specifically for the BRGs,

the SPI, and the I2C internal BRG. Alternatively, external clock pins can be configured as clock sources.

The external source option allows flexible baud-rate frequency generation, independent of the system

CLK Pin x

Clock

Source

MUX

Divide by

1 or 16

Prescaler

12-Bit Counter

1–4,096

DIV 16

CD[0–11]

BRGO

n Clock

BRGCLK

EXTC

ATB

Autobaud

Control

RXD

To Pin and/or

Bank of Clocks

BRG

CLK Pin y

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