UART学习笔记

串口(UART)

DIV_VAL = (PCLK / (bps x 16 ) ) −1

35 = 115200/66.5/16-1

查看芯片手册：

GPACON 0x7F008000 R/W Port A Configuration Register 0x0000

GPA0 [3:0] 0000 = Input 0001 = Output

0010 = UART RXD[0] 0011 = Reserved

0100 = Reserved 0101 = Reserved

0110 = Reserved 0111 = External Interrupt Group 1 [0]

0000

GPA1 [7:4] 0000 = Input 0001 = Output

0010 = UART TXD[0] 0011 = Reserved

0100 = Reserved 0101 = Reserved

0110 = Reserved 0111 = External Interrupt Group 1 [1]

0000

ULCON0 0x7F005000 R/W UART channel 0 line control register 0x00

Reserved [7] 0

Infra-Red Mode [6] Determine whether ornot to use the Infra-Red mode.

0 = Normal mode operation

1 = Infra-Red Tx/Rx mode

0

Parity Mode [5:3] Specify the type of parity generation and checking during

UART transmit and receive operation.

0xx = No parity

100 = Odd parity

101 = Even parity

110 = Parity forced/checked as 1

111 = Parity forced/checked as 0

000

Number of Stop Bit [2] Specify how many stop bits are to be used for end-of-frame

signal.

0 = One stop bit per frame

1 = Two stop bit per frame

0

Word Length [1:0] Indicate the number ofdata bits to be transmitted or received

per frame.

00 = 5-bit 01 = 6-bit

10 = 7-bit 11 = 8-bit

UCON0 0x7F005004 R/W UART channel 0 control register 0x00

Transmit Mode [3:2] Determine which function is currently able to write Tx data to the

UART transmit buffer register.

00 = Disable

01 = Interrupt request or polling mode

10 = DMA request (DMA_UART0)

11 = DMA request (DMA_UART1)

00

Receive Mode [1:0] Determine which function is currently able to read data from UART

receive buffer register.

00 = Disable

01 = Interrupt request or polling mode

10 = DMA request (DMA_UART0)

11 = DMA request (DMA_UART1)

UFCON0 0x7F005008 R/W UART channel 0 FIFO control register 0x0

FIFO Enable [0] 0 = Disable 1 = Enable 0

UMCON0 0x7F00500C R/W UART channel 0 Modem control register 0x0

DIV_VAL = UBRDIVn + (num of 1’s in UDIVSLOTn)/16

DIV_VAL = (PCLK / (bps x 16 ) ) −1

For example, if the baud-rate is 115200 bps and EXT_UCLK0 is UART baud-rate clock and 40 MHz, UBRDIVn

and UDIVSLOTn are:

DIV_VAL = (40000000 / (115200 x 16) ) -1 = 21.7 -1

= 20.7

UBRDIVn = 20 (integer part of DIV_VAL )

(num of 1’s in UDIVSLOTn)/16 = 0.7

then, (num of 1’s in UDIVSLOTn) = 11

66.5mhz*10(6)=66500000

UBRDIV0 0x7F005028 R/W Baud rate divisior register 0 0x0000

UDIVSLOT0 0x7F00502C R/W Baud rate divisior register 0 0x0000

UFSTAT0 0x7F005018 R UART channel 0 FIFO status register 0x00

Tx FIFO Full [14] Set to 1 automatically whenever transmit FIFO is full

during transmit operation

0 = 0-byte ≤Tx FIFO data ≤63-byte

1 = Full

0

Tx FIFO Count [13:8] Number of data in Tx FIFO 0

Reserved [7] 0

Rx FIFO Full [6] Set to 1 automaticallywhenever receive FIFO is full during

receive operation

0 = 0-byte ≤Rx FIFO data ≤63-byte

1 = Full

0

Rx FIFO Count [5:0] Number of data in Rx FIFO 0

URXH0 0x7F005024 R UART channel 0 receive buffer register 0x00

UTXH0 0x7F005020 W UART channel 0 transmit buffer register -

Tx FIFO Full [14] Set to 1 automatically whenever transmit FIFO is full

during transmit operation

0 = 0-byte ≤Tx FIFO data ≤63-byte

1 = Full

示例代码如下：

#define ULCON0 (*((volatile unsigned long *)0x7F005000))

#define UCON0 (*((volatile unsigned long *)0x7F005004))

#define UFCON0 (*((volatile unsigned long *)0x7F005008))

#define UMCON0 (*((volatile unsigned long *)0x7F00500C))

#define UTRSTAT0 (*((volatile unsigned long *)0x7F005010))

#define UFSTAT0 (*((volatile unsigned long *)0x7F005018))

#define UTXH0 (*((volatile unsigned char *)0x7F005020))

#define URXH0 (*((volatile unsigned char *)0x7F005024))

#define UBRDIV0 (*((volatile unsigned short *)0x7F005028))

#define UDIVSLOT0 (*((volatile unsigned short *)0x7F00502C))

#define GPACON (*((volatile unsigned long*)0x7F008000))

void init_uart(void)

{

/*将GPACON的前八位清零*/

/*1010 1010*/

/*0000 0000 （~0xff）*/

/*--------------*/

/*0000 0000*/

GPACON &= ~0xff;

/*设GPACON初值*/

GPACON |= 0x22;

/* ULCON0 */

ULCON0 = 0x3; /* 数据位:8, 无较验, 停止位: 1, 8n1 */

UCON0 = 0x5; /* 使能UART发送、接收 */

UFCON0 = 0x01; /* FIFO ENABLE */

UMCON0 = 0;

/* 波特率 */

/* DIV_VAL = (PCLK / (bps x 16 ) ) - 1

* bps = 57600

* DIV_VAL = (66500000 / (115200 x 16 ) ) - 1

* = 35.08

*/

UBRDIV0 = 35;

/* x/16 = 0.08

* x = 1

*/

UDIVSLOT0 = 0x1;

}

char getchar(void)

{

while ((UFSTAT0 & (1<<6)) == 0 && (UFSTAT0 & 0x3f) == 0);

return URXH0;

}

void putchar(char c)

{

while ((UFSTAT0 & (1<<14));

UTXH0 = c;

}