UPSD3422_V01 datasheet(109/300 Pages) STMICROELECTRONICS

109 / 300 page

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UPSD3422, UPSD3433, UPSD3434, UPSD3454

Serial UART interfaces

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21.2

Serial port control registers

The SFR SCON0 controls UART0, and SCON1 controls UART1, shown in Table 65 and

Table 67. These registers contain not only the mode selection bits, but also the 9th data bit

for transmit and receive (bits TB8 and RB8), and the UART Interrupt flags, TI and RI.

Table 65.

SCON0: serial port UART0 control register (SFR 98h, reset value 00h)

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

SM0

SM1

SM2

REN

TB8

RB8

Table 66.

SCON0 register bit definition

Bit

Symbol

R/W

Definition

SM0

R,W

Serial Mode Select, See Table 64 on page 108.

Important, notice bit order of SM0 and SM1.

[SM0:SM1] = 00b, Mode 0

[SM0:SM1] = 01b, Mode 1

[SM0:SM1] = 10b, Mode 2

[SM0:SM1] = 11b, Mode 3

6SM1

R,W

5SM2

R,W

Serial Multiprocessor Communication Enable.

Mode 0: SM2 has no effect but should remain 0.

Mode 1: If SM2 = 0 then stop bit ignored. SM2 =1 then RI active

if stop bit = 1.

Mode 2 and 3: Multiprocessor Comm Enable. If SM2=0, 9th bit

is ignored. If SM2=1, RI active when 9th bit = 1.

4REN

R,W

Receive Enable.

If REN=0, UART reception disabled. If REN=1, reception is

enabled

3TB8

R,W

TB8 is assigned to the 9th transmission bit in Mode 2 and 3. Not

used in Mode 0 and 1.

2RB8

R,W

Mode 0: RB8 is not used.

Mode 1: If SM2 = 0, the RB8 is the level of the received stop bit.

Mode 2 and 3: RB8 is the 9th data bit that was received in Mode

2 and 3.

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 67.

SCON1: serial port UART1 control register (SFR D8h, reset value 00h)

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

SM0

SM1

SM2

REN

TB8

RB8

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