/* INPUT PINS */
PIN 1 = clock; /* clock input*/
/**************** OUTPUT PINS *********************/
PIN 14 = Q1 ; /*output*/
PIN 15 = Q2 ; /*output*/
Q1.ck = clock;
Q1.d = !Q1;
Q2.d = !Q2;
This is my code and the two lines below the output pins create a 1 bit ripple counter but I'm unsure how to transfer the output of the first flip flop to be the clock input for the second flip flop. The chip I'm trying to program is an Atmel ATF750C chip.
The device does not allow separate clock definitions for individual flip-flops. The clock input to pin 1 is a shared clock for all flip-flops in the device. You could try the following instead:
Device = G16V8;
/* Inputs */
Pin 1 = CLK; /* clock source */
Pin 11 = GND; /* ground this for registered operation */
/* Outputs */
Pin 12 = Q0;
Pin 13 = Q1;
Pin 14 = Q2;
Pin 15 = Q3;
/* Equations */
!Q0.d = !Q3;
Q0.oe = 'b'1; /* output enabled - also default */
!Q1.d = Q0;
Q1.oe = 'b'1; /* output enabled - also default */
!Q2.d = Q1;
Q2.oe = 'b'1; /* output enabled - also default */
!Q3.d = Q2;
Q3.oe = 'b'1; /* output enabled - also default */
Note: The above example would provide a 4-bit ripple binary counter/divider.
For instance: An 8MHz clock input would be divided by 8 resulting in 4 shifted 1MHz outputs on each Q pin.
Wincupl is a sort of primitive vhdl, but I have now figured it out. I just had to append ".d" to my output variables, then attached my clock to pin #1 and ground pin #11. And yeah I did have to get intimate with the GAL16v8 and WinCUPL documentation to figure it all out.
/******** OUTPUT PINS **********/
PIN 14 = Q1.d;
PIN 15 = Q2.d;
Q1.ck = clock;
!Q1.d = Q1;
Q2.ck = !Q1;
!Q2.d = Q2;
This creates an asynchronous ripple counter that counts up in binary using D flip flops.
Related
I want to configure PLL in STM32F429 to its max frequency (180Mhz) without using STMCube-generated configurations. I am using my own register definitions like this
#define RCC_CFGR (*((volatile uint32 *)0x40023808))
and my own SET_BIT()/CLEAR_BIT() macros
My questions are:
1- Is this procedure correct?
2- How can I check if it is working?
3- May the MCU can not handle this speed (reading/writing in registers)?
#define PLL_M 16
#define PLL_N 360
#define PLL_P 2
#define PLL_Q 7
void PLL_init(void)
{
/* System Init */
/* HSI ON */
SET_BIT(RCC_CR, HSION);
/* Reset CFGR register */
RCC_CFGR = 0x00000000 ;
/* Reset PLLCFGR register */
RCC_PLLCFGR = 0x24003010;
/* Reset HSEON, CSSON and PLLON bits */
RCC_CR &= (uint32_t)0xFEF6FFFF;
/************* SetSysClock ************/
RCC_PLLCFGR = PLL_M | (PLL_N << 6) | (((PLL_P >> 1) -1) << 16)| (PLL_Q << 24);
/* PLL clock Source HSI or HSE */
CLEAR_BIT(RCC_PLLCFGR, PLLSRC);
/* APB1 PWR Enable*/
SET_BIT(RCC_APB1ENR, PWREN);
/* Select regulator voltage output Scale 1 mode, System frequency up to 180 MHz */
SET_BIT(PWR_CR, VOS0);
SET_BIT(PWR_CR, VOS1);
/* AHB div 1 */
CLEAR_BIT(RCC_CFGR,HPRE3);
CLEAR_BIT(RCC_CFGR,HPRE0);
/* APB2 Div = 2*/
CLEAR_BIT(RCC_CFGR,PPRE20);
CLEAR_BIT(RCC_CFGR,PPRE21);
SET_BIT(RCC_CFGR, PPRE23);
/* APB 1 Div = 8 */
CLEAR_BIT(RCC_CFGR, PPRE10);
SET_BIT(RCC_CFGR, PPRE11);
SET_BIT(RCC_CFGR, PPRE12);
/* SET PLL ON */
SET_BIT(RCC_CR, PLLON);
/* Check PLL is ready */
while(BIT_IS_CLEAR(RCC_CR,PLLRDY));
/* Enable the Over-drive to extend the clock frequency to 180 Mhz */
SET_BIT(PWR_CR, ODEN);
while(BIT_IS_CLEAR(PWR_CSR,ODRDY));
SET_BIT(PWR_CR, ODSWEN);
while(BIT_IS_CLEAR(PWR_CSR,ODSWRDY));
SET_BIT(FLASH_ACR, PRFTEN);
SET_BIT(FLASH_ACR, ICEN);
SET_BIT(FLASH_ACR, DCEN);
FLASH_ACR |= FLASH_ACR_LATENCY_5WS;
/* Select the main PLL as system clock source */
CLEAR_BIT(RCC_CFGR, SW0);
SET_BIT(RCC_CFGR, SW1);
/* Wait till the main PLL is used as system clock source */
while(!BIT_IS_CLEAR(RCC_CFGR,SWS0) && !BIT_IS_SET(RCC_CFGR,SWS1) ); /* Loop till is Set */
}
I did exactly this thing on my STM32F746 - set 216MHz with registers. It looks very similar to mine. Not observing any obvious things. You wait for all ready flags and all. Overdrive and overdrive switching are there, flash wait states are there.
How to check if it's working - timer is an easy idea. Timer that is clocked by a system clock with some prescaler and that outputs PWM to some pin. Given the configuration of the timer is set by you, you should know what output frequency to expect. You can set timer parameters in such a way that you expect timer-interrupt-toggle an LED every 1s.
The MCU should handle it OK if all prescalers for AHB/APB are within limits, as well as Flash latency is set correctly. Which seems to be the case.
If you want to compare the logic with what I do with STM32F746 (which looks almost identical in terms of how you do it), you can check it in this rcc.c file of mine. It definitely works, I tested it.
I am working on a weird problem: As a part of my project, I migrated a firmware from CooCox to TrueStudio. Both, CooCox and TrueStudio automatically create some standard files while creating a project for a specific Microcontroller. The Microcontroller used here is the STM32F407VGT6. I am using ms - delay and s - delay which are derived from the µs - Delay function I will show you.
*edit2: I should mention, that the original project is a pure C project. I am trying to make the Project a C++/C project in TrueStudio.
What I will try now is to migrate the firmware into a TrueStudio pure C project and see if the problem still exists.
I will inform you about the results
**Results: The problem is actually gone now in the pure C Project, but I would really like to implement classes etc using C++. Any ideas how to solve this?
**
*
The initializing systick code is (HCLK Frequency = 168MHz).
*edit1: the HCLK Frequency equals the SYSCLK *
void systick_init(void){
RCC_ClocksTypeDef RCC_Clocks;
Systick_Delay=0;
RCC_GetClocksFreq(&RCC_Clocks);
SysTick_Config((RCC_Clocks.HCLK_Frequency / 1000000) - 1);
}
The function for the 1µs Delay looks like this:
void delay_us(volatile uint32_t delay)
{
Systick_Delay = delay;
while(Systick_Delay != 0);
}
The Systick Handler contains the following Code:
void SysTick_Handler(void)
{
// Tick für Delay
if(Systick_Delay != 0x00)
{
Systick_Delay--;
}
}
When I create a .hex file to flash the µC with using Coocox, the timing function works (with some minor accuracy mistakes that don't bother me).
When I create the .hex file with TrueStudio, the delays have massive inaccuracys. For example, a delay of 500ms becomes a delay of roughly 2s.
Since the Code is written dependant on the actual HCLK_Frequency, I can't understand the mistake and in my understanding, even if the HCLK should differ, the 1µs Delay should still take about 1µs.
My next step will be comparing the automatically created system files, but maybe anyone has a different approach / another idea?
*edit 3: I normally include my systick - header with the command ' extern "C" '. So my systick source file is a .c file. When I rename the file to systick.cpp, and I include the header without 'extern "C"', the delay function does not work at all. Maybe, that helps with the solution?
*
You are either running off a different clock or have different PLL settings. Looks like your clock speed is 1/4 of what you had before.
The basic startup code provided does not always set the maximum speed for the board. Have a look in some of the examples in the stm32cube.zip code. You will find some System Clock Configuration code for your board which will select the correct clock and pll settings. (this will be in your code somewhere as well).
Look in main.c under stm32cubef4/projects/STM32F4-Discovery\Demonstrations\src.
You will find the following code which sets up the clock:
/**
* #brief System Clock Configuration
* The system Clock is configured as follow :
* System Clock source = PLL (HSE)
* SYSCLK(Hz) = 168000000
* HCLK(Hz) = 168000000
* AHB Prescaler = 1
* APB1 Prescaler = 4
* APB2 Prescaler = 2
* HSE Frequency(Hz) = 8000000
* PLL_M = 8
* PLL_N = 336
* PLL_P = 2
* PLL_Q = 7
* VDD(V) = 3.3
* Main regulator output voltage = Scale1 mode
* Flash Latency(WS) = 5
* #param None
* #retval None
*/
static void SystemClock_Config(void)
{
RCC_ClkInitTypeDef RCC_ClkInitStruct;
RCC_OscInitTypeDef RCC_OscInitStruct;
/* Enable Power Control clock */
__HAL_RCC_PWR_CLK_ENABLE();
/* The voltage scaling allows optimizing the power consumption when the device is
clocked below the maximum system frequency, to update the voltage scaling value
regarding system frequency refer to product datasheet. */
__HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE1);
/* Enable HSE Oscillator and activate PLL with HSE as source */
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
RCC_OscInitStruct.HSEState = RCC_HSE_ON;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
RCC_OscInitStruct.PLL.PLLM = 8;
RCC_OscInitStruct.PLL.PLLN = 336;
RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2;
RCC_OscInitStruct.PLL.PLLQ = 7;
HAL_RCC_OscConfig(&RCC_OscInitStruct);
/* Select PLL as system clock source and configure the HCLK, PCLK1 and PCLK2
clocks dividers */
RCC_ClkInitStruct.ClockType = (RCC_CLOCKTYPE_SYSCLK | RCC_CLOCKTYPE_HCLK | RCC_CLOCKTYPE_PCLK1 | RCC_CLOCKTYPE_PCLK2);
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV4;
RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV2;
HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_5);
/* STM32F405x/407x/415x/417x Revision Z devices: prefetch is supported */
if (HAL_GetREVID() == 0x1001)
{
/* Enable the Flash prefetch */
__HAL_FLASH_PREFETCH_BUFFER_ENABLE();
}
}
I found the solution now!
For anyone having similar problems:
You need to declare the SysTick_Handler function as
extern "C" void SysTick_Handler(void)
{
//Tick für Delay
if(Systick_Delay != 0x00)
{
Systick_Delay--;
}
}
Now it is working like it is supposed to do.
I am working with the explorer16/32 evb and trying to send data to UART.
I tried UART1, UART2 with and without interrupts and got the same problem all the time.
It appeared that in order to send 1 byte I need to split it to two 4 bits with shift
code:
#define FCY 16000000
#define BAUDRATE 9600
#define BRGVAL ((FCY/BAUDRATE)/16)-1
U2MODE = 0;
U2STA = 0;
U2MODEbits.STSEL = 0; // 1-Stop bit
U2MODEbits.PDSEL = 0 ; // No Parity 8 bit data
U2MODEbits.ABAUD = 0; // Auto-Baud Disabled
U2MODEbits.BRGH = 1; // High Speed Mode
U2MODEbits.URXINV = 0;
U2STAbits.UTXINV = 0;
U2BRG = BRGVAL; // Baud Rate Setting for 9600
U2MODEbits.UARTEN = 1; //Enable UART module
U2STAbits.UTXEN = 1; //Enable UART TX
unsigned char putU2(unsigned char c)
{
while (U2STAbits.TRMT == 0)
{
}
while ( CTS);
while ( U2STAbits.UTXBF);
U2TXREG = c & 0xF;
U2TXREG = (c >> 4) & 0xF;
return c;
}
If I am sedning that data splited to 4 bits I can see the data correct on the PC( c# serial port application)
But it should not be split into two writes to U2TXREG.
I am not 100% sure that the FCY is 16000000 but this is the only value that give me reasonable result.
What could be the problem?
For PIC24H, in UART high speed mode ( BRGH = 1 ) to get correct value of BRGVAL you need to divide by 4, not 16. Change the formula on line 3. Also, it is helpful to be 100% sure about clock rate; if you didn't change configuration bits it is likely 8 MHz, not 16.
I am currently working for the first time with a PIC microcontroller. In the code I specified exactly which PIC, compiler, etc I am using. Maybe this is of help.
I am trying to set up UART communication on the PIC32 and send a hex code like 0x41 for example to a terminal on my computer through RS232. To convert the signal from the PIC UART to RS232 levels I am using a MAX232EPE.
At the moment I am running into the problem that when I send 0x41 for example from the PIC32 to the terminal or vice versa, the received data doesn't match. I think this being caused by a mistake in my baud rate settings, but I am not sure. Could someone please look over my code and see if someone can see a problem? Did I forget to define something? Did I define something wrong? Did I mis calculate the baud rate?
P.S. I know the data being received doesn't match the data send because i checked in the "watches" in debug mode in mplab and when I echo the data send from the terminal to the PIC32 back to the terminal it doesn't match either.
The Delay and interrupt code can be ignored, they are working as expected, so I really believe the problem has to do with the initial setting of the PIC/buad rate.
I hope this is clear enough, any help is very much appreciated
Thanks,
See code below
/*
The configuration below and in void UART1_Init should set up the UART correctly.
I want to achieve a buadrate of 9600. My external Crystal is 8MHz. So:
FPLLIDIV=2, FPLLMUL=20, FPLLODIV=1, FPBDIV=2, FNOSC=PRIPLL, BRGH = 0, and U1BRG = 259.
This should give me the desired baudrate of 9600.
- ((8MHz / 2) * 20)/2) = 40MHz PBclk.
- U1BRG = (PBclk/(16*Buad rate))-1 so 259
- 16*Buad rate because BRGH = 0
PIC32MX795F512H
MPLAB X IDE V3.26
XC32 Compiler
PICKit3
*/
#include <stdio.h>
#include <stdlib.h>
#include <xc.h>
#include <plib.h>
// Give useful names to pins
#define LED1_TRIS TRISDbits.TRISD6
#define LED1 LATDbits.LATD6
#define UART1TX_TRIS TRISDbits.TRISD3
#define UART1RX_TRIS TRISDbits.TRISD2
#define FOSC 8000000 // Crystal frequency = 8 MHz
#define SYS_FREQ (80000000UL) // SYSCLK is 80 MHz
#define GetSystemClock() (FOSC) // For delay
#pragma config FPLLIDIV=DIV_2 // PLL Input Divider Value (Divide by 2)
#pragma config FPLLMUL=MUL_20 // Phase-Locked Loop (PPL) muiltiplier, multiplier of 20
#pragma config FPLLODIV=DIV_1 // Postscaler for PLL, output divided by 1
#pragma config FPBDIV=DIV_2 // 2 = PBCLK is SYSCLK divided by 2 (80MHz/2 = 40MHz)
#pragma config FWDTEN=OFF // Watch Dog Timer (WDT) is not enabled. It can be enabled by software
#pragma config CP=OFF // Code-Protect, 1 = OFF/Disabled
#pragma config BWP=OFF // Boot Flash Write-protect, 1 = OFF/Disabled
#pragma config POSCMOD=XT // Primary oscillator configuration, HS = HS Oscillator mode selection
#pragma config FNOSC=PRIPLL // Oscillator selection, PRIPLL = Primary Oscillator with PLL module
#pragma config OSCIOFNC=OFF // CLKO output disabled
#pragma config FSOSCEN=OFF // Disable secondary Oscillator
int UART_RX_Count; // Counter variable for the UART1 receiver interrupt
int UART_TX_Count; // Counter varible for the UART1 transmitted interrupt
unsigned char RD_SER_NUM; // Variable to store command to read serial number
unsigned char UART_RX_OUTPUT; // Variable to store the UART output
unsigned char i;
void UART1_Init(void){
// UART1 initialization
U1MODEbits.ON = 1; // UART1 is enabled
U1MODEbits.SIDL = 0; // Continue operation in idle mode
U1MODEbits.IREN = 0; // Disable IrDA (IrDA Encoder and Decoder Enable bit)
U1MODEbits.RTSMD = 1; // !U1RTS! pin is in Simplex mode, 0 = !U1RTS! pin is in Flow Control mode
U1MODEbits.UEN = 0; // UxTX and UxRX pins are enabled and used; UxCTS and UxRTS/UxBCLK pins are controlled by corresponding bits in the PORTx register
U1MODEbits.WAKE = 1; // Enable Wake-up on Start bit Detect During Sleep Mode bit
U1MODEbits.LPBACK = 0; // UARTx Loopback Mode Select bit, 0 = disabled, loopback = UxTX output is internally connected to the UxRX input
U1MODEbits.PDSEL = 2; // Parity and Data Selection bits, 10 = 8-bit data, odd parity
U1MODEbits.STSEL = 0; // Stop Selection bit, 0 = 1 stop bit
U1MODEbits.BRGH = 0; // High Baud Rate Enable bit, 0 = Standard Speed mode 16x baud clock enabled
U1MODEbits.RXINV = 1; // Receive Polarity Inversion bit, 1 = UxRX Idle state is 0
U1STAbits.URXEN = 1; // 1 = UART1 receiver is enabled. U1RX pin is controlled by UARTx (if ON = 1)
U1STAbits.UTXEN = 1; // 1 = UART1 transmitter is enabled. U1TX pin is controlled by UARTx (if ON = 1)
U1STAbits.UTXINV = 1; // Transmit Polarity Inversion bit, 1 = UxTX Idle state is 0
U1STAbits.ADM_EN = 0; // 0 = Automatic Address Detect mode is disabled
U1BRG = 259; // Baud Rate Divisor bits (0-15 bits), set baud rate, 9600 # 40 MHz PBclk
__builtin_disable_interrupts(); // Tell CPU to stop paying attention to interrupts
INTCONbits.MVEC = 1; // Multi Vector interrupts
U1STAbits.URXISEL = 0; // 0x = Interrupt flag bit is set when a character is received
U1STAbits.UTXISEL = 1; // 01 = Interrupt flag bit is set when all characters have been transmitted
IPC6bits.U1IP = 5; // Set UART1 priority 5 of 7
IPC6bits.U1IS = 0; // Set UART1 sub priority to 0
IFS0bits.U1RXIF = 0; // Clear UART1 RX interrupt flag
IFS0bits.U1TXIF = 0; // Clear UART1 TX interrupt flag
IEC0bits.U1RXIE = 1; // Enable UART1 RX ISR
__builtin_enable_interrupts(); // Tell CPU to start paying attention to interrupts again
UART_RX_Count = 0; // Set initial UART1 received interrupts count to 0
UART_TX_Count = 0; // Set initial UART1 transmit interrupts count to 0
}
void __ISR(_UART_1_VECTOR, IPL5SRS) UART1_INT(void){
if(INTGetFlag(INT_U1RX)){ // Check if UART1 RX interrupt was triggered
LED1 = ~LED1; // Toggle LED1
UART_RX_Count++; // Add 1 to UART1 RX interrupt occurrence counter
// UART_RX_OUTPUT = U1RXREG; // Read UART1 RX buffer/register
U1TXREG = U1RXREG; // Transmit the received data back
// U1STAbits.OERR = 0; // Clear UART1 buffer overflow
IFS0bits.U1RXIF = 0; // Clear UART1 RX interrupt flag
}else{
if(INTGetFlag(INT_U1TX)){ // Check if UART1 TX interrupt was triggered
UART_TX_Count++; // Add 1 to UART1 TX interrupt occurrence counter
IEC0bits.U1TXIE = 0; // Disable UART1 TX ISR
IFS0bits.U1TXIF = 0; // Clear UART1 TX interrupt flag
}
}
}
// DelayMs creates a delay of given milliseconds using the Core Timer
void DelayMs(WORD delay){
unsigned int int_status;
while( delay-- ){
int_status = INTDisableInterrupts();
OpenCoreTimer(GetSystemClock() / 200);
INTRestoreInterrupts(int_status);
mCTClearIntFlag();
while( !mCTGetIntFlag() );
}
mCTClearIntFlag();
}
int main(){
UART1_Init(); // Call the initializations function of UART1
LED1_TRIS = 0; // Set the LED1 as an output
UART1TX_TRIS = 0; // Set UART1 TX pin as output
UART1RX_TRIS = 1; // Set UART1 RX pin as input
LED1 = 0; // Turn off LED1
while(1){
// DelayMs(1000);
// IEC0bits.U1TXIE = 1; // Enable UART1 TX ISR
// U1TXREG = 0x41; // Send command to U1TXREG
}
return 0;
}
As You are using PIC32MX795F512H, You can use the MPLAB Harmony framework tool for creating your project. So that you need not to play on bit level and stuck in minor error or most probabaly typo error.
Its convinient to generate drivers and all framework properly.
Thanks and regards
Ravi
Using Harmony will actually help you avoid simple errors like the one you have encountered. Especially for the clocks you even have auto calculating functions decreasing your implementation time significantly.
I am trying to read several PWM signals from an RC receiver into an ATMega 2560. I am having trouble understanding how the ICRn pin functions as it appears to be used for all three compare registers.
The RC PWM signal has a period of 20ms with a HIGH pulse of 2ms being a valid upper value and 1ms being a valid lower value. So the value will sweep from 1000us to 2000us. The period should begin at the rising edge of the pulse.
I have prescaled the 16MHz clock by 8 to have a 2MHz timer an thus should be able to measure the signal to 0.5us accuracy which is sufficient for my requirements.
Please note that I am having not problems with PWM output and this question is specifically about PWM input.
My code thus far is attached below. I know that I will have to use ICR3 and an ISR to measure the PWM values but I am unsure as to the best procedure for doing this. I also do not know how to check if the value measured is from PE3, PE4, or PE5. Is this code right and how do I get the value that I am looking for?
Any help would be greatly appreciated.
// Set pins as inputs
DDRE |= ( 0 << PE3 ) | ( 0 << PE4 ) | ( 0 << PE5 );
// Configure Timers for CTC mode
TCCR3A |= ( 1 << WGM31 ) | ( 1 << WGM30 ); // Set on compare match
TCCR3B |= ( 1 << WGM33 ) | ( 1 << WGM32 ) | ( 1 << CS31); // Set on compare match, prescale_clk/8
TCCR3B |= ( 1 << ICES5 ) // Use rising edge as trigger
// 16 bit register - set TOP value
OCR3A = 40000 - 1;
OCR3B = 40000 - 1;
OCR3C = 40000 - 1;
TIMSK3 |= ( 1 << ICIE3 );
I had forgotten to post my solution a few months ago so here it is...
I used a PPM receiver in the end so this code can easily edited to read a simple PWM.
In my header file I made a structure for a 6 channel receiver that I was using for my project. This can be changed as required for receivers with more or less channels.
#ifndef _PPM_H_
#define _PPM_H_
// Libraries included
#include <stdint.h>
#include <avr/interrupt.h>
struct orangeRX_ppm {
uint16_t ch[6];
};
volatile unsigned char ch_index;
struct orangeRX_ppm ppm;
/* Functions */
void ppm_input_init(void); // Initialise the PPM Input to CTC mode
ISR( TIMER5_CAPT_vect ); // Use ISR to handle CTC interrupt and decode PPM
#endif /* _PPM_H_ */
I then had the following in my .c file.
// Libraries included
#include <avr/io.h>
#include <stdint.h>
#include "ppm.h"
/* PPM INPUT
* ---
* ICP5 Pin48 on Arduino Mega
*/
void ppm_input_init(void)
{
DDRL |= ( 0 << PL1 ); // set ICP5 as an input
TCCR5A = 0x00; // none
TCCR5B = ( 1 << ICES5 ) | ( 1 << CS51); // use rising edge as trigger, prescale_clk/8
TIMSK5 = ( 1 << ICIE5 ); // allow input capture interrupts
// Clear timer 5
TCNT5H = 0x00;
TCNT5L = 0x00;
}
// Interrupt service routine for reading PPM values from the radio receiver.
ISR( TIMER5_CAPT_vect )
{
// Count duration of the high pulse
uint16_t high_cnt;
high_cnt = (unsigned int)ICR5L;
high_cnt += (unsigned int)ICR5H * 256;
/* If the duration is greater than 5000 counts then this is the end of the PPM signal
* and the next signal being addressed will be Ch0
*/
if ( high_cnt < 5000 )
{
// Added for security of the array
if ( ch_index > 5 )
{
ch_index = 5;
}
ppm.ch[ch_index] = high_cnt; // Write channel value to array
ch_index++; // increment channel index
}
else
{
ch_index = 0; // reset channel index
}
// Reset counter
TCNT5H = 0;
TCNT5L = 0;
TIFR5 = ( 1 << ICF5 ); // clear input capture flag
}
This code will use an trigger an ISR every time ICP5 goes from low to high. In this ISR the 16bit ICR5 register "ICR5H<<8|ICR5L" holds the number of pre-scaled clock pulses that have elapsed since the last change from low to high. This count is typically less than 2000 us. I have said that if the count is greater than 2500us (5000 counts) then the input is invalid and the next input should be ppm.ch[0].
I have attached an image of PPM as seen on my oscilloscope.
This method of reading PPM is quite efficient as we do not need to keep polling pins to check their logic level.
Don't forget to enable interrupts using the sei() command. Otherwise the ISR will never run.
Let's say you want to do the following (I'm not saying this will allow you to accurately measure the PWM signals but it might serve as example on how to set the registers)
Three timers running, which reset every 20 ms. This can be done by setting them in CTC mode for OCRnA: wgm3..0 = 0b0100.
//timer 1
TCCR4A = 0;
TCCR1B = (1<<CS11) | (1<<WGM12);
OCR1A = 40000 - 1;
//timer 3 (there's no ICP2)
TCCR3A = 0;
TCCR3B = (1<<CS31) | (1<<WGM32);
OCR3A = 40000 - 1;
//timer 4
TCCR4A = 0;
TCCR4B = (1<<CS41) | (1<<WGM42);
OCR4A = 40000 - 1;
Now connect each of the three pwm signals to their own ICPn pin (where n = timer). Check the datasheet for the locations of the different ICPn pins (i'm pretty sure it's not PE3, 4, 5)
Assuming the pwm signals start high at t=0 and go low after their high-time for the remainder of the period. You want to measure the high-time so we trigger an interrupt for each when a falling edge occurs on the ICPn pin.
bit ICESn in the TCCRnB register set to 0 will select the falling edge (this is already done in the previous code block).
To trigger the interrupts, set the corresponding interrupt enable bits:
TIMSK1 |= (1<<ICIE1);
TIMSK3 |= (1<<ICIE3);
TIMSK4 |= (1<<ICIE4);
sei();
Now each time an interrupt is triggered for ICn you can grab the ICRn register to see the time (in clockperiods/8) at which the falling edge occurred.