ELECTRONICS - [BK1786B supply] - [hardware addon] - [page 4/4]

BK1786B Hardware Addon

The used tools

I wrote the software for the microcontroller in the C programming language, using Microchip's MPLAB IDE and the High-Tech C compiler toolsuite. They can be downloaded for free from Microchip's website. I programmed the microcontroller with my Olimex USB PIC programmer [External].

PIC program

Here you can find the complete firmware for the PIC.

/***************************************************************** * BK Instruments Polling Device * * Copyright (c) 2012 * Vanderhaegen Bart * * * This device will instruct the PIC16F628 to read and poll the * BK Instrument every 100 milliseconds to detect an over-current. * * *****************************************************************/ // Includes #include "htc.h"; // Definitions #define _XTAL_FREQ 19668000 #define PACKET_SIZE 26 #define PACKET_ADDR 0 #define LED_OK RB0 #define LED_ERR RB5 #define BUZZER RB6 // Variable Declarations char packetTransmit[PACKET_SIZE]; // transmission buffer char packetReceived[PACKET_SIZE]; // receive buffer char receiveCounter=0; // number of received bytes // Declaration of the error flags bit framingErrorOccured=0; bit invalidFrameLengthOccured=0; bit invalidCheckSumOccured=0; bit invalidResponseOccured=0; bit frameReceived=0; // checkSum() returns the checksum of the received data char checkSum(void) { int checkSum=0; for (char i=0;i<PACKET_SIZE-2;i++) { checkSum+=packetReceived[i]; } return checkSum % 256; } // is_bit_set checks if a certain bit of a byte is 1 or 0. bit is_bit_set(char value, char bitindex) { if ((value & (1 << bitindex)) != 0) return 1; else return 0; } // processResponse() processes the packets when they are received. void processResponse() { frameReceived=1; if (receiveCounter==PACKET_SIZE) { if (checkSum()==packetReceived[PACKET_SIZE-1]) { // data valid (right length & checksum matches) LED_OK=!LED_OK; LED_ERR=0; if (packetReceived[2]==0x26) { // Evaluate CC & CV mode if(is_bit_set(packetReceived[9],3)==1) BUZZER=1; else BUZZER=0; } else { invalidResponseOccured=1; } } else { // Error: invalid checksum invalidCheckSumOccured=1; } } else { // Error: invalid data length invalidFrameLengthOccured=1; } } static void interrupt isr( void ) { if (RCIF) { if (FERR==1) { // A framing error occured. framingErrorOccured=1; FERR=0; } // check the overrun error bit if (OERR==1) { CREN=0; CREN=1; } // Receive the data packet packetReceived[receiveCounter]=RCREG; receiveCounter++; // stop receiving data when 26 bytes are received if (receiveCounter>=PACKET_SIZE) { processResponse(); receiveCounter=0; } } } // sendRequest() will send the request frame to the BK unit. void sendRequest(void) { TXEN=1; for (char i=0;i<PACKET_SIZE;i++) { while(TXIF==0); TXREG=packetTransmit[i]; } receiveCounter=0; } // initUART() will initialise the UART of the PIC // The baud rate is set to baud 9600, the X-TAL is 19.668 MHz. void initUART() { // Configure the baud rate SPBRG = 127; // baud rate generator register BRGH = 1; // Enable high baud-rate // Enable asynchronous communication SYNC = 0; // Asynchronous mode SPEN = 1; // Enable serial port TRISB1 = 1; // Required by UART (datasheet) TRISB2 = 1; // Required by UART (datasheet) // Enable 8-bit data words TX9 = 0; RX9 = 0; // Enable Interrupts RCIE = 1; // enable USART interrupt CREN = 1; // Continuous recieve enable bit : ENABLE PEIE = 1; // enable unmasked periheral interrupts GIE = 1; // global interrupt enable } // executeStartupTest() runs a small test when starting the PIC. void executeStartupTest() { // Execute startup test for (char i=0;i<4;i++) { __delay_ms(100); LED_OK=1; LED_ERR=1; BUZZER=1; __delay_ms(100); LED_OK=0; LED_ERR=0; BUZZER=0; } } // flashError() flashes the LEDs for a number of times. void flashError(char numberOfFlashes) { LED_ERR=0; for (char i=0;i<numberOfFlashes;i++) { LED_ERR=!LED_ERR; __delay_ms(500); } __delay_ms(1000); } // pollErrorFags() will trigger the error LEDs // Note: in the current program only one error can occur at once. void pollErrorFlags() { if (frameReceived==0) flashError(2); // no response if (framingErrorOccured==1) flashError(4); // framing errors (RS-232 error) if (invalidFrameLengthOccured==1) flashError(6); // invalid frame received if (invalidCheckSumOccured==1) flashError(8); // invalid checksum calculated if (invalidResponseOccured==1) flashError(10); // invalid response } // initTransmissionPacket() will prepare the packetTransmit array. void initTransmissionPacket() { for (char i=0;i<PACKET_SIZE;i++) packetTransmit[i]=0; packetTransmit[0]=0xAA; packetTransmit[2]=0x26; packetTransmit[25]=0xD0; } // MAIN PROGRAM void main() { // Initialisation of the I/O TRISB = 0x00; PORTB = 0x00; // Initialisation of the UART initUART(); // initialisation of the data packet initTransmissionPacket(); // Execute startup test executeStartupTest(); // Main program loop // This loop is cycled until the end of days while(1) { // Reset the LEDs FERR=0; LED_OK=0; LED_ERR=0; // Reset the error messages framingErrorOccured=0; invalidFrameLengthOccured=0; invalidCheckSumOccured=0; invalidResponseOccured=0; frameReceived=0; // Send a request to the BK unit sendRequest(); // Add a delay before executing the next cycle. // Data is received during this delay (interrupts) __delay_ms(100); // poll the error flags pollErrorFlags(); } }

Function of the program

The program uses the asynchronous mode of the PIC's USART (Universal Synchronous Asynchronous Receiver Transmitter). The hardware baud rate is preset to 9600. The hardware address is set to 0x00. Please make sure these settings match the actual settings of your BK unit!

The PIC will transmit a request frame each 100 milliseconds. Then it will wait for the next cycle. It uses this waiting time to receive and process any data from the BK unit. Each time a byte is received, an interrupt (TXIF) is triggered. The interrupt handler will then build a data array containing all the received bytes.

After the reception of the 26^th byte, the software function processResponse() is called. This function will validate the received data. During the validation process the frame length, checksum and response code are verified. Once the data has been validated successfully, the 10^th data byte is analyzed. This byte contains the state of the power supply unit. The third bit of this byte will be evaluated and the PIC will start the orange output LED if this bit is "1". (See Part2 : Communication Aspects for more information about the protocol)

Error codes

My circuit uses a RED flashing LED to indicate any errors. I have implemented 5 different error codes:

1 flash: no response from the BK unit (check connection, hardware address).
2 flashes: a framing error occurred (RS-232 communication error, check baud rate).
3 flashes: the BK unit replied with a packet with an invalid length.
4 flashes: the BK unit replied with a packet with a wrong checksum.
5 flashes: the BK unit replied with a wrong packet.

Download

Download the PIC source code for this project. The code comes in a ZIP file with the complete MPLAB project.

Download PIC source code