UM0851 datasheet(99/245 Pages) STMICROELECTRONICS

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UM0851

Communication device drivers

Doc ID 16604 Rev 2

99/245

fractional number enabling you to use any clock with a frequency >3.6864 MHz as the

reference clock.

●

Standard asynchronous communication bits (start, stop and parity). These are added

prior to transmission and removed on reception.

●

Support for direct memory access (DMA).

●

Support of the modem control functions CTS, DCD, DSR, RTS, DTR, and RI.

●

Programmable hardware flow control.

●

Fully-programmable serial interface characteristics:

–

Data can be 5, 6, 7, or 8 bits

–

Even, odd, stick, or no-parity bit generation and detection

–

1 or 2 stop bit generation

–

Baud rate generation, dc up to UARTCLK_max_freq/16

The most common use of the UART is to communicate to a PC serial port using the RS-232

(recommended standard 232) protocol.

RS-232 is a standard electrical interface for serial communications. RS-232 actually comes

in 3 different flavors (A, B, and C) with each one defining a different voltage range for the on

and off levels. The most commonly used variety is RS-232C, which defines a mark (on) bit

as a voltage between -3V and -12V and a space (off) bit as a voltage between +3V and

+12V.

Figure 25.

The interface between UART and RS-232

4.8.2

Software overview

UART drivers service another kernel layer, the TTY layer. I/O system calls start their journey

above top-level line disciplines and finally ripple down to UART drivers through the TTY

layer.

The data flow between the user space and the serial device driver, therefore, is mediated by

the TTY layer, that implements functionalities that are common to all TTY-type devices.

APB

Interface

UART

RS-232

RTS

DTR

DSR

RXD

TXD

CTS

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