UPSD3312D datasheet(110/272 Pages) STMICROELECTRONICS

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UPSD33xx

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Doc ID 9685 Rev 7

21.3

UART baud rates

The baud rate in mode 0 is fixed:

Mode 0 Baud Rate = fOSC / 12

The baud rate in mode 2 depends on the value of the bit SMOD in the SFR named PCON. If

SMOD = 0 (default value), the baud rate is 1/64 the oscillator frequency, fOSC. If SMOD = 1,

the baud rate is 1/32 the oscillator frequency.

Mode 2 Baud Rate = (2SMOD / 64) x fOSC

Baud rates in modes 1 and 3 are determined by the Timer 1 or Timer 2 overflow rate.

21.3.1

Using Timer 1 to generate baud rates

When Timer 1 is used as the baud rate generator (bits RCLK = 0, TCLK = 0), the baud rates

in modes 1 and 3 are determined by the Timer 1 overflow rate and the value of SMOD as

follows:

Mode 1,3 Baud Rate =

(2SMOD / 32) x (Timer 1 overflow rate)

The Timer 1 Interrupt should be disabled in this application. The Timer itself can be

configured for either “timer” or “counter” operation, and in any of its 3 running modes. In the

most typical applications, it is configured for “timer” operation, in the Auto-reload mode (high

nibble of the SFR TMOD = 0010B). In that case the baud rate is given by the formula:

Mode 1,3 Baud Rate =

(2SMOD / 32) x (fOSC / (12 x [256 – (TH1)]))

Table 67 on page 111 lists various commonly used baud rates and how they can be

obtained from Timer 1.

1TI

R,W

Transmit Interrupt flag.

Causes interrupt at end of 8th bit time when transmitting in

mode 0, or at beginning of stop bit transmission in other

modes. Must clear flag with firmware.

0RI

R,W

Receive Interrupt flag.

Causes interrupt at end of 8th bit time when receiving in

mode 0, or halfway through stop bit reception in other modes

(see SM2 for exception). Must clear this flag with firmware.

Table 66.

SCON1 register bit definition (continued)

Bit

Symbol

R/W

Definition

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