SN250 datasheet(45/130 Pages) STMICROELECTRONICS

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SN250

Functional description—application modules

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7.2.1

UART mode

The SC1 UART controller is enabled with SC1_MODE set to 1.

The UART mode contains the following features:

●

Baud rate (300 bps up to 921 Kbps)

●

Data bits (7 or 8)

●

Parity bits (none, odd, or even)

●

Stop bits (1 or 2)

The following signals can be made available on GPIO pins:

●

TXD

●

RXD

●

nRTS (optional)

●

nCTS (optional)

The SC1 UART module obtains its reference baud-rate clock from a programmable baud

generator. Baud rates are set by a clock division ratio from the 24MHz clock:

rate = 24MHz / ( 2

∗ ( N + (0.5 ∗ F) ) )

The integer portion, N, is written to the SC1_UARTPER register and the fractional remainder,

F, to the SC1_UARTFRAC register. Table 19 lists the supported baud rates with associated

baud rate error. The minimum allowable setting for SC1_UARTPER is 8.

The UART module supports various frame formats depending upon the number of data bits

(SC1_UART8BIT), the number of stop bits (SC1_UART2STP), and the parity (SC1_UARTPAR

plus SC1_UARTODD). The register bits SC1_UART8BIT, SC1_UART2STP, SC1_UARTPAR,

and SC1_UARTODD are defined within the SC1_UARTCFG register. In addition, the UART

module supports flow control by setting SC1_UARTFLOW, SC1_UARTAUTO, and

SC1_UARTRTS

in the SC1_UARTCFG register (see Table 20).

Table 19.

UART baud rates

Baud Rate (bps)

SC1_UARTPER

SC1_UARTFRAC

Baud Rate Error (%)

300

40000

4800

2500

9600

1250

19200

625

38400

312

57600

208

− 0.08

115200

104

0.16

460800

0.16

921600

0.16

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