//Open Timer1 with 1:8 prescaler (80MHz -> 10MHz), with period of 10, therefore tick = 1MHz. OpenTimer1(T1_ON | T1_PS_1_8 | T1_SOURCE_INT, 10); ConfigIntTimer1(T1_INT_ON | T1_INT_PRIOR_2); INTEnableSystemMultiVectoredInt();And the interrupt handler:
void __ISR(_TIMER_1_VECTOR, ipl2) _Timer1Handler(void) {
mT1ClearIntFlag();
//Your code
}
void __ISR(_CHANGE_NOTICE_VECTOR, ipl2) ChangeNotice_Handler(void) {
mPORTDRead(); //Need to read the port (see PIC32 datasheet)
mCNClearIntFlag();
//Your code...
}
mCNOpen(CN_ON | CN_IDLE_CON, CN13_ENABLE | CN14_ENABLE | CN15_ENABLE, CN_PULLUP_DISABLE_ALL); //See plib documentation and PIC32 datasheet ConfigIntCN(CHANGE_INT_ON | CHANGE_INT_PRI_2); INTEnableSystemMultiVectoredInt();
FreeRTOS is a really cool real-time operating system (preemptive scheduler) for various architectures. It has been ported to the PIC18 platform (using MPLAB C18 compiler). However, the port is not very good.
Isaac Marino Bavaresco (isaacbavaresco AT yahoo DOT com DOT br) of the PICLIST has greatly improved and optimized the port for PIC18. His PICLIST page is here.
It took me a long time to get everything set up and working properly, so I’m writing this tutorial as an easy quick-start guide on getting FreeRTOS running on the PIC18.
Things you’ll need to get started:
Step 1 – Setting up your directories
Configure your directories in this structure:
Step 2 – Download FreeRTOS_mod for PIC18 from the link above.
Unzip in your projects directory and you will get a directory named “FreeRTOS”.
Step 3 – Create a project
Explanation
All that this project does is create two tasks that constantly print “abcd” and “1234” to the UART. It uses a mutex to ensure that the non-thread-safe puts function is only being used in one thread at a time.
The RTOS configuration file is FreeRTOSConfig.h. The only thing non-standard in there is the #define CUSTOM_HEAP macro. I created this little modification to replace the standard malloc()/free() calls in the RTOS source to instead use Isaac’s functions which are far more optimized.
With a lot of help from Isaac Marino Bavaresco (PICLIST), I finally got FreeRTOS up and running perfectly on my PIC18F2620. It’s a fun chip loaded with features and perfect for FreeRTOS. I’ll write a complete tutorial shortly to get the RTOS working on this chip. Hopefully, when I get my dsPIC33 and PIC32, it will be a whole lot easier to get the RTOS working.
I recently started a project which required several microcontrollers (placed around the house) to be able to communicate with each other. The difficult part is choosing a communications method and protocol. After doing some research, I found the following to be suitable options for inter-microcontroller communications.
The most interesting and suitable option I found was was the RS485 bus. This bus allows for communications over potentially long distances (greater than 1.3 km), tolerates high speed, allows for many protocol designs, is asynchronous and easy to use. Several protocols allow for multiple bus masters with collision detection. Overall, the bus should be pretty reliable. Further research suggested that either CAT3 (phone cable) can be used with 6 contact RJ11 type connectors. This allows for full duplex communication over 4 lines and one ground line. CAT 5 ethernet cable with RJ45 type connectors could also be used if desired. However, twisted pair cable is strongly recommended (such as CAT3 or CAT5).
Another option is using ethernet. The Microchip ENC26J60 transceiver can be used. However, I’m not sure how ethernet can be used as a bus (without a hub/switch). More on this later.
If wires prove to be too cumbersome to implement, one may chose to take the wireless route. Futurlec sells SPI radio transceiver modules at a low cost. Implement your own protocol.
Other busses such as CAN, LIN and USB are further discussed on the following site: http://www.ucpros.com/
The best hobby chips are: (spaces added in part numbers for readability)
The 18F26J50 definitely seems cool. Note that the 46 models (as opposed to the 26 models) have higher pin counts and therefore, more ADC channels. Both come in DIP packages – very hobby friendly. The only trouble with the 18F26J50 is that it has a maximum voltage of 3.3 V.
The PIC18 series have a maximum internal oscillator frequency of 8 MHz, which translates to 2 MIPS. However, the PIC can run at much higher speeds (especially when using an external clock source). Using the PIC's PLL, one is able to multiply the clock source by up to 4 times. This is even software-controllable if using the internal clock source. Using the maximum speed of the internal oscillator, the PIC can run at up to 32 MHZ with PLL enabled. This yields blazing fast performance of 8 MIPS. Best of all, you can turn this feature on or off as you please to control power consumption. Using the PLL is very easy.
We must first ensure that we are using the internal oscillator. So, in C18, declare a configuration option like this:
#pragma config OSC = INTIO67
Next, we must either configure the internal oscillator to run at 4 or 8 MHz. The PLL will not be enabled on any other configuration. Since we're opting for speed here, let's set it at 8 MHz. Put the following as the first line in your main() function:
OSCCON = 0b01110000;
Note that the last two bits of OSCCON must be 00. And finally, to enable the PLL, add the next line right after:
OSCTUNE = 0b01011111;
This enables the PLL and runs the PIC at the maximum possible frequency using only the internal oscillator - 8 MIPS @ 32 MHz. To toggle the PLL on or off, simply set OSCTUNEbits.PLLEN to either 1 or 0, respectively. Refer to the datasheet for information on how to fine-tune the PLL.