Difference between revisions of "GPS RECEIVER - MT3329"

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::*This is only test software. No buffer to hold unread data
 
::*This is only test software. No buffer to hold unread data
 
<source lang=c>
 
<source lang=c>
−
USART1
+
int main (void) {
−
CLOCK = PCLK1 AFTER APB1 PRESCALER
 
  
−
BaudRate =   fck / ( 16 * USARTDIV )
+
   SystemInit();                            /* initialize clocks            */
  
−
Fx:
+
  /* Setup GPIO for LEDs                                                    */
−
   fck = 72 Mhz
+
   RCC->APB2ENR |= 1 <<  6;                /* Enable GPIOE clock            */
−
   Wanted BuadRate = 9.600
+
   GPIOE->CRH    = 0x33333333;              /* Configure the GPIO for LEDs  */
  
−
   USARTDIV = fck/ (16 * BaudRate ) =
+
   GLCD_Init();                              /* Initialize the GLCD          */
−
    72000000/ (16 * 9600) = 468,75
+
  GLCD_Clear(White);                        /* Clear the GLCD                */
−
 
+
−
Mantissa = 438 - as hex = 0x1D4
+
//Enable Port B clock and configure USART1 (with remapping of USART1 to Port B from Port A)
−
Fraction = 16*0.75 = 6 - as hex 0xC
+
RCC->APB2ENR |= 1 << 3;
−
*/
+
RCC->CFGR |= 4 << 10;
−
void usart1_enable( void) {
+
RCC->APB2ENR |= 1 << 0;
−
//Step  1: RCC_APB2ENR - Enable Clock for Port B
+
AFIO->MAPR |= 1 << 2;
−
rcc_apb2enr(1 << 3,ENABLE);
+
−
 
+
//Enable GPIOB7 as rx, GPIOB6 as tx (Pin7: 0100, Pin6: 1011)
−
//Step 2: RCC_CFGR bits PPRE1[2:0] = 100 -APB1 Prescaler divide by 2 = 36 MHz
+
  GPIOB->CRL &= 0x00FFFFFF;
−
rcc_cfgr( 0x00000300, 0 ); //Set PPRE1[1:0] = 0
+
  GPIOB->CRL |= 0x4B000000;
−
rcc_cfgr( 0x00000400, 1 ); //Set PPRE1[2] = 1
+
−
 
+
//Enable USART in RCC_APB2ENR
−
//Step  3: RCC_APB2ENR - Enable AFIO Clock - Alternate Clock I/O Enable
+
RCC->APB2ENR |= 1 << 14;
−
rcc_apb2enr(1 << 0,ENABLE);
+
−
 
+
/*
−
//Step  4: AFIO_MAPR - Remap USART1  to Port B
+
Set baud rate (USART_BRR): BaudRate =  fck / ( 16 * USARTDIV )
−
rcc_afio_mapr(1 << 2, ENABLE);
+
For example:
−
 
+
fck = 72 MHz
−
//Step 5.1 and 5.2 - Enable pin 7 as RX and pin 6 as TX
+
required Baud Rate = 9600
−
GPIOB->CRL &= 0x00FFFFFF;
+
−
GPIOB->CRL |= 0x4B000000;   //Pin 7: 0100 Pin 6: 1011
+
USARTDIV = fck/(16 * BaudRate ) = 72000000/(16 * 9600) = 468.75
−
 
+
−
//Step  6: RCC Enable USART in RCC_APB2ENR
+
Mantissa = 438 - as hex: 0x1D4
−
rcc_apb2enr( 1 << 14, ENABLE); //set bit 14 in RCC_APB2ENR (Enable USART1)
+
Fraction = 16*0.75 = 12 - as hex: 0xC
−
 
+
−
//Step  7.1 and 7.2: USART_BRR bits DIV_Mantissa[11:0] = 0x1d4 and fraction = c
+
See Reference Manual for further details
−
USART1->BRR = 0x01d4c;
+
*/
−
 
+
USART1->BRR = 0x01d4c;
−
//Step  8: USART_CR1 bit UE - Uart Enable = 1
+
−
USART1->CR1 |= 1 << 13;
+
//USART enable
−
 
+
USART1->CR1 |= 1 << 13;
−
//Step 13: USART_CR1 bit TE - Tranmitter enable = 1
+
−
USART1->CR1 |= 1 << 3;
+
//USART Tx enable
−
 
+
USART1->CR1 |= 1 << 3;
−
//Step 14: USART_CR1 bit RE - Receiver enable = 1
+
−
USART1->CR1 |= 1 << 2;
+
//USART Rx enable
−
 
+
USART1->CR1 |= 1 << 2;
−
//Step 15: USART_CR1 bit RXNEIE - Receiver interrupt enable = 1
+
−
USART1->CR1 |= 1 << 5;
+
//USART Rx Interrupt enable
 +
USART1->CR1 |= 1 << 5;
 +
 +
//Send initialisation messages to the GPS, 1: Baud rate, 2: Reset GPS to output default NMEA messages
 +
putstr("PMTK251,9600*17\r\n");
 +
putstr("PMTK314,-1*04\r\n");
 +
 +
NVIC_EnableIRQ(USART1_IRQn);
  
 +
        os_sys_init (init);                      /* Initialize RTX and start init */
 
}
 
}
  

Revision as of 09:17, 22 October 2014

Module on MCBSTM32C Keil board

Picture 1: GPS Module attached to Keil board. (Click to enlarge)
Picture 2: Wires attached between Keil board and 6 pin connecter. Display removed. (Click to enlarge)
Picture 3: GPS Module attached to 6 pin connector on Keil board.(Click to enlarge)

Using the STM32F107VC remapped USART1 to PB6 (USART1_TX)and PB7 (USART1_RX). The GPS module uses VCC and GND and not RS232 levels on TX/RX. Five boards are modified for the five GPS modules bought.

  • The [1] show that PB6 is used for CAN2 bus TX. CAN2 bus can't be used at the same time as the GPS module.
  • The [2] show that PB7 is used for the USER button. To use PB7 as RX from the GPS module it is necessary to remove C20. The USER switch can't be used at the same time as the GPS module.

Connections

Solder a 6 pin 0,1 inch 90 degrees angle. See picture 2 and connect

  • Pin 1 to 3,3V (Red wire)
  • Pin 2 to GND (Black wire)
  • Pin 3 - Not used in this project ( 1 second pulse signal from GPS module )
  • Pin 4 to PB7 (Orange wire) - GPS module TX
  • Pin 5 to PB6 (Yellow wire) - GPS module RX
  • Pin 6 - NOt used in this project ( FIX signal )

Battery connector on keil board

The minus pole on the battery has no electrical connection to the main board. To make a connection a desisolated wire was placed between the minuspole on the battery and the goldplated area on the PCB under the battery. See picture 2.

USART 1 code

To communicate with the GPS module the following code gives access to USART 1.

NOTE
The example below is a codesnippet from the test code. The usart1_rx function should be called from an RTX thread called t_gps.
  • This is only test software. No buffer to hold unread data
int main (void) {

  SystemInit();                             /* initialize clocks             */

  /* Setup GPIO for LEDs                                                     */
  RCC->APB2ENR |=  1 <<  6;                 /* Enable GPIOE clock            */
  GPIOE->CRH    = 0x33333333;               /* Configure the GPIO for LEDs   */

  GLCD_Init();                              /* Initialize the GLCD           */
  GLCD_Clear(White);                        /* Clear the GLCD                */
	
	//Enable Port B clock and configure USART1 (with remapping of USART1 to Port B from Port A)
	RCC->APB2ENR |= 1 << 3;
	RCC->CFGR  |= 4 << 10;
	RCC->APB2ENR |= 1 << 0;
	AFIO->MAPR |= 1 << 2;
	
	//Enable GPIOB7 as rx, GPIOB6 as tx (Pin7: 0100, Pin6: 1011)
  GPIOB->CRL &= 0x00FFFFFF;
  GPIOB->CRL |= 0x4B000000;	
	
	//Enable USART in RCC_APB2ENR
	RCC->APB2ENR |= 1 << 14;
	
	/*
	Set baud rate (USART_BRR): BaudRate =   fck / ( 16 * USARTDIV )
		For example:
			fck = 72 MHz
			required Baud Rate = 9600
		 
			USARTDIV = fck/(16 * BaudRate ) = 72000000/(16 * 9600) = 468.75
		 
			Mantissa = 438 - as hex: 0x1D4
			Fraction = 16*0.75 = 12 - as hex: 0xC
			
			See Reference Manual for further details
	*/ 
	USART1->BRR = 0x01d4c;
	
	//USART enable
	USART1->CR1 |= 1 << 13;
	
	//USART Tx enable
	USART1->CR1 |= 1 << 3;
	
	//USART Rx enable
	USART1->CR1 |= 1 << 2;
	
	//USART Rx Interrupt enable
	USART1->CR1 |= 1 << 5;
	
	//Send initialisation messages to the GPS, 1: Baud rate, 2: Reset GPS to output default NMEA messages
	putstr("PMTK251,9600*17\r\n");
	putstr("PMTK314,-1*04\r\n");
	
	NVIC_EnableIRQ(USART1_IRQn);

        os_sys_init (init);                       /* Initialize RTX and start init */
}

void usart1_tx( char character ) {
	while ((USART1->SR & ( 1 << 6)) == 0) {}; // Wait HSERDY = 1
	USART1->DR = (uint16_t) character;
}
void putstr(char *string) {
	int i;
	for ( i=0; string[i] != 0; i++ ) {
		usart1_tx(string[i]);
	}
}

//Receive
char usart1_rx() {
	os_evt_wait_and (0x0001, 0xffff);
	return(USART1->DR);
}

void USART1_IRQHandler( void ) __irq {
	
	isr_evt_set(0x0001, t_gps); 
	while ((USART1->SR & ( 1 << 5)) == 0) {}; // Wait RXNE = 1

}

Data sheets

ARM board projects


Links

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