![Steps to Configure GPIO
Enable the power
Set Pins and their modes
• Selecting the GPIO LPC_PINCON->PINSEL[0-4]
• Input/output direction LPC_GPIO[0-2]->FIODIR
Set appropriate interrupts if needed
• Raising/falling edge LPC_GPIOINT->IO2IntEnF
• Registering NVIC_EnableIRQ( EINT3_IRQn )
• Clearing interrupt LPC_GPIOINT->IO2IntClr
Manipulating the pins
• Set an output pin FIOSET
• Read an input pin FIOPIN
• Clear an output pin FIOCLR
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How to use peripherals on MCB1700
- 1. How to use peripherals on MCB1700 MTE241 – Fall2014
- 2. Peripherals • GPIO • ADC/DAC • Ethernet • USB 6/23/2016 MTE241 – Fall2014 2(UM10360, 2014)
- 3. Power Control Block Power is a major concern in ARM-based chips • By powering down the unused peripherals, considerable power is saved Peripheral power control register is referenced from CMISIS as LPC_SC->PCONP • LPC_SC is a general system-control register block • PCONP refers to Power CONtrol for Peripherals µVision provides the peripherals power through system_17xx.c 6/23/2016 MTE241 – Fall2014 3
- 4. Pin Connect Block Most chip pins can perform up to four different functions • You must specify what function you want each pin to be used for Programming a set of registers known as the Pin Connect Block • From CMSIS as a struct called LPC_PINCON, with fields called PINSEL1, PINSEL2, PINMODE1, PINMODE2 and so on. 6/23/2016 MTE241 – Fall2014 4 (UM10360, 2014) (UM10360, 2014)
- 5. Interrupt Service Routine • Almost all Peripherals can generate interrupts. • The conditions on generating interrupts are different for each peripherals. • Interrupt Service Routines in CMIS is just a function with the interrupt source appended by _IRQHandler • E.g. ADC_IRQHandler • CMIS provides APIs for enabling/disabling, prioritizing, and Pending ISRs: • Interrupts can be fired by writing interrupt number in NVIC->STIR • But, they are cleared depending on the peripherals caused. void NVIC_EnableIRQ( IRQn_Type IRQn ) void NVIC_DisableIRQ( IRQn_Type IRQn ) void NVIC_SetPriority( IRQn_Type IRQn, int32_t priority ) uint32_t NVIC_GetPriority( IRQn_Type IRQn ) 6/23/2016 MTE241 – Fall2014 5
- 6. The chip directly communicates with its environment through pins in GPIO mode • The pin can be set for input or output directions • In case of MCB1700: • 8 LEDs are connected as output pins • Joystick and INT0 button are connected as input pins General-Purpose I/O 6/23/2016 MTE241 – Fall2014 6
- 7. Steps to Configure GPIO Enable the power Set Pins and their modes • Selecting the GPIO LPC_PINCON->PINSEL[0-4] • Input/output direction LPC_GPIO[0-2]->FIODIR Set appropriate interrupts if needed • Raising/falling edge LPC_GPIOINT->IO2IntEnF • Registering NVIC_EnableIRQ( EINT3_IRQn ) • Clearing interrupt LPC_GPIOINT->IO2IntClr Manipulating the pins • Set an output pin FIOSET • Read an input pin FIOPIN • Clear an output pin FIOCLR 6/23/2016 MTE241 – Fall2014 7
- 8. Example 1: Turning On/Off a LED 1) Enable power LPC_SC->PCONP |= (1 << 15); 2) LED connected to p1.28 is in GPIO mode LPC_PINCON->PINSEL3 &= ~(3 << 25); 3) LED connected to p1.28 is an output pin LPC_GPIO1->FIODIR |= (1 << 28); 4) Turning on the LED LPC_GPIO1->FIOSET |= (1 << 28); 5) Turning off the LED LPC_GPIO1->FIOCLR |= (1 << 28); 6/23/2016 MTE241 – Fall2014 8 (UM10360, 2014)
- 9. Example 2: Intercepting push-button click 1) Enable power 2) Push-button connected to p2.10 is in GPIO mode LPC_PINCON->PINSEL4 &= ~( 3 << 20 ); 3) P2.10 is an input pin LPC_GPIO2->FIODIR &= ~( 1 << 10 ); 4) P2.10 reads the falling edges to generate an interrupt LPC_GPIOINT->IO2IntEnF |= ( 1 << 10 ); 5) IRQ is enabled in NVIC. NVIC_EnableIRQ( EINT3_IRQn ); 6) Clear interrupt condition when it has been fired LPC_GPIOINT->IO2IntClr |= (1 << 10); 6/23/2016 MTE241 – Fall2014 9
- 10. Clocks • Clock in LPC178 is very flexible to generate different frequencies at the same time • Clock source is selected through Clock Source Select register LPC_SC->CLKSRCSEL: • Internal 4 MHz RC oscillator (this is the default) • 12 MHz external oscillator • 32 kHz real-time clock oscillator • The input clock is directly fed into PLL to increase the clock frequency and clock divider to decrease the clock • The clock can be divided further for peripheral clockSetup the PLL and frequency devisors is complex and involves many registers • µVision provides a straightforward interface to set the clock through system_17xx.c 6/23/2016 MTE241 – Fall2014 10 (UM10360, 2014)
- 11. Configuring the clock • Select the Main oscillator • The main oscillator generates 12 MHz clock, OSCRANGE has to cover it. • Select PLL0 to accelerate the clock • The output frequency of PLL is 2 × M × F ÷ N • F is input frequency • 6 ≤ M ≤ 512 • 1 ≤ N ≤ 32 • E.g., 400 MHz = 2 × 100 × 12 ÷ 6 • Pick a proper clock divider for 100 MHz ARM • CCLKSEL = 4 • Now the clock are ready for peripherals in 100 MHz, 50 MHz, 25 MHz and 12.5 MHz 6/23/2016 MTE241 – Fall2014 11
- 12. Analogue to Digital Convertor • A 12-bit analog to digital converter • 8 converting channels through 8-input analog mux • A potentiometer connected to analog input 2 • Three registers are particularly to be configured • The analog/digital control register LPC_ADC->ADCR • The analog/digital global data register LPC_ADC->ADGDR • The analog/digital interrupt enable register LPC_ADC->ADINTEN 6/23/2016 MTE241 – Fall2014 12
- 13. ADC configuration steps • Set Power using PCONP register • Where is accessible in system_17xx.c • Set Clock using PCLKSEL0 register • Already set • Enable ADC0 pins through PINSEL registers • Enable interrupts using CMSIS APIs • Now, start conversion. • Wait until the ADC status shows the conversion is done after ~52 ticks. • Response to the interrupt 6/23/2016 MTE241 – Fall2014 13
- 14. Example3: Reading Potentiometer 1) Enable power LPC_SC->PCONP |= ( 1 << 12 ); 2) Potentiometer connected to p0.25 is in ADC mode LPC_PINCON->PINSEL1 &= ~( 0x3 << 18 ); //clear bits LPC_PINCON->PINSEL1 |= ( 0x1 << 18 ); //set bits 3) Set the ADC control register LPC_ADC->ADCR = ( 1 << 2 ) | // Select the second channel ( 4 << 8 ) | // ADC clock is 25MHz/(4+1) ( 0 << 24 ) | // Do not start the conversion yet ( 1 << 21 ); // Enable ADC 4) Enable interrupt for all ADC channels LPC_ADC->ADINTEN = ( 1 << 8); 5) Register interrupt NVIC_EnableIRQ( ADC_IRQn ); 6) Start Conversion LPC_ADC->ADCR |= ( 1 << 24 ); LPC_SC->PCONP |= ( 1 << 12 ); 7) Read the converted value I. Polling (i.e. busy waiting) to see when the conversion is done. There is no need to activate and register interrupts in this way. // wait for conversion complete while (LPC->ADGDR & 0x8000 == 0); // read 12 bits result ADC_Value = (LPC_ADC->ADGDR>>4) & 0xFFF; II. Response for the interrupt // Read ADC Status clears the interrupt condition aDCStat = LPC_ADC->ADSTAT; ADC_Value = (LPC_ADC->ADGDR >> 4) & 0xFFF; 6/23/2016 MTE241 – Fall2014 14
- 15. Resources • LPC176x/5x User manual. (2014, April 2014). 3.1, 846. NXP Semiconductor. Retrieved November 1, 2014, from http://www.nxp.com/documents/user_manual/UM10360.pdf • Roehl, B. (2011, April 18). Lab Manual for ECE 455. 39. Waterloo, ON, Canada. Retrieved November 1, 2014, from http://www.arm.com/files/pdf/ece455labmanual_preliminary.pdf • Yiu, J. (2009). The Definitive Guide to the ARM® Cortex-M3 6/23/2016 MTE241 – Fall2014 15 @MANUAL {lpc178:usermanual, title = "UM10360: LPC176x/5x User manual", organization = "NXP Semiconductor", edition = "Rev.3.1", month = "apr", year = "2014" }