DAN-201 Datasheet, PDF (1/4 Pages) Exar Corporation – INDEPENDENT TX AND RX BAUD RATE GENERATOR

APRIL 2009
DATA COMMUNICATIONS APPLICATION NOTE
DAN 201
INDEPENDENT TX AND RX BAUD RATE GENERATOR
1.0 INTRODUCTION
This application note describes the independent TX and RX baud rate generator feature of Exar’s new low
power and high speed XR16Mxxx single channel UART family.
2.0 BAUD RATE GENERATOR (BRG)
2.1 PREVIOUS BAUD RATE GENERATOR ON UARTS
The TX and RX of previous generation UARTs share the same baud rate generator, as shown in Figure 1. For
the same channel, TX and RX always run at the same baud rate. That is, setting up DLL, DLM & DLD registers
(some UARTs don’t have DLD register) actually decide the data rate for both TX and RX.
FIGURE 1. BAUD RATE GENERATOR ON PREVIOUS GENERATION UARTS
XTAL1
XTAL2
To Other
Channels
Crystal
Osc/
Buffer
Prescaler
Divide by 1
Prescaler
Divide by 4
DLL, DLM and DLD
Registers
MCR Bit-7=0
(default)
Fractional Baud
Rate Generator
Logic
16X or 8X or 4X
Sampling
Rate Clock
to Transmitter
and Receiver
MCR Bit-7=1
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • [phone] • FAX [phone] • www.exar.com