DATA COMMUNICATIONS APPLICATION NOTE

2

DAN 201

The XR16Mxxx single channel UART family has the independent baud rate generator feature. Thus, the trans-

mitter and receiver can run at different baud rates (see Figure 2). DLL, DLM and DLD needs to be initialized

for both TX and RX.

XTAL1

XTAL2

/

-

(default)

16X or 8X or 4X

Sampling Rate Clock

Prescaler

Divide by 1

Prescaler

Divide by 4

MCR Bit 7= 0

MCR Bit -7=1

Crystal

Osc

Buffer

DLL

DLM

DLD[5:0]

DLL

DLM

DLD[5:0]

16X or 8X or 4X

Sampling Rate Clock

DLD[7]=0

DLD[7]=1

0

1

DLD[6]

By default, the TX and RX uses the same BRG. Different BRGs can be enabled by DLD[6]. While initializing,

DLD[7] selects the BRG that is being configured.

3.0 PROGRAMMING FOR INDEPENDENT TX AND RX BAUD RATE GENERATOR

By setting DLD, XR16Mxxx single channel UART family can operate transmitter (TX) and receiver (RX) in

different baud rate. The following examples show different set-ups. The first 2 examples use the same baud

rate generator (BRG) for both TX and RX. Others use different BRGs for TX and RX.

This example uses the default 16X sampling rate and the default BRG prescaler value 1 for both TX and RX.

write(LCR, 0xBF);

write(EFR, 0x10);

//EFR[4] = 1 to enable the access of DLD

write(LCR,0x80);

write(DLD, 0x0);

//TX and RX use same BRG

write(DLL, 0x1);

write(DLM, 0x0);

write(LCR, 0x3);

//Set data format 8 data bit and 1 stop bit

This example uses the 8X sampling rate and the default BRG prescaler value 1 for both TX and RX.

write(LCR, 0xBF);

write(EFR, 0x10);

//EFR[4] = 1 to enable the access of DLD

write(LCR, 0x80);

write(DLD, 0x14);

//TX and RX use same BRG; Enable 8X mode;Set the fractional baud rate

write(DLL, 0x3);

write(DLM, 0x0);

write(LCR, 0x3);

//Set data format 8 data bit and 1 stop bit