UART初始化：prevent UART拉RTS高 [英] UART initialisation: Prevent UART to pull RTS high

问题描述

我在写Linux上的ARM AT91SAM9260板RS485驱动程序。

I'm writing a RS485 driver for an ARM AT91SAM9260 board on Linux.

当我初始化UART，RTS信号线变高（1）。我想这将并应在RS232操作模式的标准行为。在RS485方式然而，这是不想要的。

When I initialise the UART, the RTS signal line gets high (1). I guess this would and should be the standard behaviour in RS232 operation mode. In RS485 mode however this is not wanted.

我使用的胳膊拱部分提供初始化UART的标准功能。因此，显著步骤是：

I'm using the standard functions provided by the arm-arch section to initialise the UART. Therefore the significant steps are:

at91_register_uart(AT91SAM9260_ID_US2, 3, ATMEL_UART_CTS | ATMEL_UART_RTS);
//consisting of:

// >> configure/mux the pins
    at91_set_A_periph(AT91_PIN_PB10, 1);        /* TXD */
    at91_set_A_periph(AT91_PIN_PB11, 0);        /* RXD */

    if (pins & ATMEL_UART_RTS)
        at91_set_B_periph(AT91_PIN_PC8, 0);     /* RTS */
    if (pins & ATMEL_UART_CTS)
        at91_set_B_periph(AT91_PIN_PC10, 0);    /* CTS */

// >> associate the clock
axm_clock_associate("usart3_clk", &pdev->dev, "usart");

// >> et voilà

正如你可以看到用

As you can see with

at91_set_B_periph（AT91_PIN_PC8，0）;

at91_set_B_periph(AT91_PIN_PC8, 0);

RTS管脚上上拉没有被激活。

the pull-up on the RTS pin isn't activated.

• 为什么UART设置RTS高呢？
  只是因为这将是标准
  在RS232模式行为？

• Why does the UART set the RTS high? Just because this would be the standard behaviour in RS232 mode?

那岂不是一个更好的标准
UART的保持沉默，直到结果
操作模式明确设置？

Wouldn't it be a better standard for the UART to keep silent till the
operation mode is explicitly set?

推荐答案

初始化后，似乎是在许多平台上的标准行为的高RTS信号。这取决于男子汉其中串行操作模式的启动例程预期的接口。

A high RTS signal after initialisation seems to be the standard behaviour on many platforms. It manly depends which serial operation mode the start-up routines anticipates for the interface.

要prevent RTS高上ATMEL AT91SAM9260板上运行Linux，你必须把UART到正确的模式之前流合并at91_set_X_periph（）的引脚和注册设备。

To prevent RTS-high on a ATMEL AT91SAM9260 board running Linux, you have to put the UART into the right mode BEFORE muxing at91_set_X_periph() the Pins and register the device.

由于Linux内核2.6.35版本的的 支持RS485方式ATMEL串口驱动程序。在此驱动程序的UART引脚（GPIO）设置有角色之前，正确配置。

Since Linux Kernel Version 2.6.35, the ATMEL serial driver supports the RS485 mode. In this driver the UART is properly configured before setting the Pins (GPIO) to there role.

对于运行较旧版本的Linux嵌入式我的设备，我解决了这个问题，下面一行的codeS：

For my embedded device which is running an older Linux version, I solved the problem with the following line of codes:

/* write control flags */

control |= ATMEL_US_RTSEN;
mode |= ATMEL_US_USMODE_RS485;  

  UART_PUT(uartbaseaddr, ATMEL_US_CR, control);
  UART_PUT(uartbaseaddr, ATMEL_US_MR,mode);

现在，这些引脚可以复用的自己的角色

Now the Pins can be muxed the their role

at91_set_X_periph（RTS_PIN，0）;

at91_set_X_periph(RTS_PIN, 0);

这篇关于UART初始化：prevent UART拉RTS高的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！