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;
}
