CAN Bus Project Part 6 - The MCP2551

This is part 6 of my project to get my Arduino (/Genuino) and TI Launchpad to communicate via CAN.

Previously I've described getting my Arduino (/Genuino) to spit out CAN messages. Today I want to start talking about having the Launchpad receive them.

An Arduino/Genuino attempting to "talk CAN" faces two problems: Firstly, CAN is fairly complex; Trying to code all the CAN logic into an Arduino would be a hefty challenge. Second, even with the correct logic, an Arduino’s pins are physically incapable of generating the fancy ("dominant / recessive") voltages CAN needs.

Fortunately, the MCP2515 from Microchip solves both problems: Your Genuino talks to it (using SPI), and it translates your messages to CAN.

Unlike the Arduino, the Lauchpad comes with CANBus logic built-in (formally, it has 2 x CAN 2.0 A/B controllers) – so you don't need an external MCP2515 IC. 

In common with the Arduino however, the Lauchpad still can't generate the ("dominant/recessive") voltages CAN needs. So, whilst you don't need external CAN logic, you do need an IC to generate CAN voltages. A Microchip MCP2551 (High Speed CAN transceiver) is a suitable choice. It translates CAN voltage levels at its CANH / CANL pins into traditional "high/low” data on its RX pin.

An issue with using the MCP2515 is that it's a 5V device. Whilst this is o.k. for the Arduino, TI Launchpad pins are limited to 3.3V. It's common in electronics to need to shift the voltage level of signals and there're lots of solutions. I used an SN74LVC245A (Octal Bus Transceiver) IC to do the 3.3-to-5V conversion (mostly as I had one lying around).

To make it easy to connect things at the Launchpad-end of the CAN bus, I wire-wrapped the MCP2551, the SN74LVC245A, and some headers together on a vero-board – see photo. You can see one of the CAN termination resistors (explanation here) at the top of the frame.

If you've been following these posts, you'll know we now have all the hardware and Arduino sofware needed to bring a CAN message right up to the Launchpad pins. All that's needed now is to configure the internals of the Lauchpad... see you next time!

CAN Bus Project part 3 : The MCP2515

Part 3 of my Arduino / Tiva CAN project...



In my previous post I generated some temperature data. Today I want to talk about transferring this from Arduino to CAN.

I'll talk about the nitty-gritty of the CAN protocol in a future post. For now, its enough to know two things: 

1. A CANBus uses 2 wires (green and orange in picture above)
2. An Arduino can't generate the funky ("dominant / recessive") voltages CAN needs!

The second point means you need an IC to translate Arduino to CAN. Microchip do the MCP2515. I found the little board in photo 1 cheap on eBay (I've no connection to the company. This isn't a plug!). 

The idea behind the MCP2515 is that you send it your data using good ol' fashioned SPI, and it spits it out as CAN messages. 




That's the theory anyway. In practice, getting CAN up-and-running isn't trivial. The problem is that before devices can share a CAN link, they need to agree on a bunch of technical details. That means agreeing things like data-rates and setting up so-called message masks that let devices know which messages are meant for them.

Configuring the (e.g.) data-rate of a CAN link means having the Arduino write certain values to certain registers on the MCP2515 during start-up. The MCP2515 has a dozen+ of these registers with catchy names like BFPCTRL. I spent a thrilling Sunday typing them all into a file (see below and also on my gitHub page). I also wrote some Arduino functions to help with sending commands to the MCP2515. 

I'm going leave things there for now. Next time, I'll describe in more detail how to use the code to set up the MCP2515.

	* Voltage Bias - the Blog. * Gilbert Waltoon
	*
	* Released under a GNU General Public License v3.0
	*
	* FILENAME: MCP2515_Registers.h
	* PURPOSE: REGISTERS AND UTILITIES FOR MCP2515 CAN CONTROLLER
	*
	*
	* VERSION 0
	* VERSION 1 21May2016
	* - Added check4Errs() function
	* - Modified readStatusIns() and rxStatusIns() to remove second (repeated) read
	*
	*/
	// Define CS pin for SPI
	#define chipSelectPin 7
	// Define some common data types
	typedef const byte tRegAddr;
	typedef const byte tMask;
	typedef const byte tIns;
	typedef const byte tBitMask;
	//Foward declaration of handy MCP2515 functions/utlities.
	//See the SPI-Interface section of the MCP2515 datasheet for full details.
	void resetIns(); //Reset the MCP2515
	byte readIns(tRegAddr); //Read an MCP2515 register. Returns the value in the register 'tRegAddr'
	byte readRxBuffIns(tIns); //Fast read of MCP2515 RX buffer. Returns value read. Possible arguments are READ_RXB0SIDH_INS, READ_RXB0D0_INS, READ_RXB1SIDH_INS, READ_RXB0D0_INS
	void writeIns(tRegAddr, byte); //Write 'byte' to MCP2515 register 'tRegAddr'
	void ldTxBuffIns(tIns, byte); //Fast write of 'byte' to the MCP2515 TX buffer. Possible 'tIns' arguments are LD_TXB0SIDH_INS, LD_TXB0D0_INS, LD_TXB1SIDH_INS, LD_TXB1D0_INS, LD_TXB2SIDH_INS LD_TXB2D0_INS
	void rqstToSendIns(tIns); //Request MCP2515 to send the message sitting in trasmit-buffer 'tIns'.
	void bitModifyIns(tRegAddr, tMask, tMask); //Modify register bits. 1st argument is register. 2nd argument is the bits to modify. 3rd argument is new bit values to write.
	byte readStatusIns(); //Fast access to selected register bits.
	byte rxStatusIns(); //Fast access to status information on messages received.
	bool check4Errs(); //Print list of CAN errors on serial port. Returns TRUE is errors occurred.
	bool setMode(String); //Select MCP2515 mode. Possible arguments are "Normal" "Sleep" "Loopback" "Listen" "Configuration". Returns TRUE if successful.
	/*
	* *****************************************************
	* MCP2515 Registers follow
	*/
	tRegAddr RXF0SIDH = 0b00000000;
	tRegAddr RXF0SIDL = 0b00000001;
	tRegAddr RXF0EIDB = 0b00000010;
	tRegAddr RXF0EID0 = 0b00000011;
	tRegAddr RXF1SIDH = 0b00000100;
	tRegAddr RXF1SIDL = 0b00000101;
	tRegAddr RXF1EID8 = 0b00000110;
	tRegAddr RXF1EID0 = 0b00000111;
	tRegAddr RXF2SIDH = 0b00001000;
	tRegAddr RXF2SIDL = 0b00001001;
	tRegAddr RXF2EID8 = 0b00001010;
	tRegAddr RXF2EID0 = 0b00001011;
	tRegAddr BFPCTRL = 0b00001100;
	tRegAddr TXRTSCTRL = 0b00001101;
	tRegAddr CANSTAT = 0b00001110;
	tRegAddr CANCTRL = 0b00001111;
	tRegAddr RXF3SIDH = 0b00010000;
	tRegAddr RXF3SIDL = 0b00010001;
	tRegAddr RXF3EIDB = 0b00010010;
	tRegAddr RXF3EID0 = 0b00010011;
	tRegAddr RXF4SIDH = 0b00010100;
	tRegAddr RXF4SIDL = 0b00010101;
	tRegAddr RXF4EID8 = 0b00010110;
	tRegAddr RXF4EID0 = 0b00010111;
	tRegAddr RXF5SIDH = 0b00011000;
	tRegAddr RXF5SIDL = 0b00011001;
	tRegAddr RXF5EID8 = 0b00011010;
	tRegAddr RXF5EID0 = 0b00011011;
	tRegAddr TEC = 0b00011100;
	tRegAddr REC = 0b00011101;
	tRegAddr RXM0SIDH = 0b00100000;
	tRegAddr RXM0SIDL = 0b00100001;
	tRegAddr RXM0EIDB = 0b00100010;
	tRegAddr RXM0EID0 = 0b00100011;
	tRegAddr RXM1SIDH = 0b00100100;
	tRegAddr RXM1SIDL = 0b00100101;
	tRegAddr RXM1EID8 = 0b00100110;
	tRegAddr RXM1EID0 = 0b00100111;
	tRegAddr CANF3 = 0b00101000;
	tRegAddr CANF2 = 0b00101001;
	tRegAddr CANF1 = 0b00101010;
	tRegAddr CANINTE = 0b00101011;
	tRegAddr CANINTF = 0b00101100;
	tRegAddr EFLG = 0b00101101;
	tRegAddr TXB0CTRL = 0b00110000;
	tRegAddr TXB0SIDH = 0b00110001;
	tRegAddr TXB0SIDL = 0x32;
	tRegAddr TXB0EIDB = 0b00110011;
	tRegAddr TXB0EID0 = 0b00110100;
	tRegAddr TXB0DLC = 0b00110101;
	tRegAddr TXB0D0 = 0b00110110;
	tRegAddr TXB0D1 = 0b00110111;
	tRegAddr TXB0D2 = 0b00111000;
	tRegAddr TXB0D3 = 0b00111001;
	tRegAddr TXB0D4 = 0b00111010;
	tRegAddr TXB0D5 = 0b00111011;
	tRegAddr TXB0D6 = 0b00111100;
	tRegAddr TXB0D7 = 0b00111101;
	tRegAddr TXB1CTRL = 0b01000000;
	tRegAddr TXB1SIDH = 0b01000001;
	tRegAddr TXB1SIDL = 0b01000010;
	tRegAddr TXB1EIDB = 0b01000011;
	tRegAddr TXB1EID0 = 0b01000100;
	tRegAddr TXB1DLC = 0b01000101;
	tRegAddr TXB1D0 = 0b01000110;
	tRegAddr TXB1D1 = 0b01000111;
	tRegAddr TXB1D2 = 0b01001000;
	tRegAddr TXB1D3 = 0b01001001;
	tRegAddr TXB1D4 = 0b01001010;
	tRegAddr TXB1D5 = 0b01001011;
	tRegAddr TXB1D6 = 0b01001100;
	tRegAddr TXB1D7 = 0b01001101;
	tRegAddr TXB2CTRL = 0b01010000;
	tRegAddr TXB2SIDH = 0b01010001;
	tRegAddr TXB2SIDL = 0b01010010;
	tRegAddr TXB2EIDB = 0b01010011;
	tRegAddr TXB2EID0 = 0b01010100;
	tRegAddr TXB2DLC = 0b01010101;
	tRegAddr TXB2D0 = 0b01010110;
	tRegAddr TXB2D1 = 0b01010111;
	tRegAddr TXB2D2 = 0b01011000;
	tRegAddr TXB2D3 = 0b01011001;
	tRegAddr TXB2D4 = 0b01011010;
	tRegAddr TXB2D5 = 0b01011011;
	tRegAddr TXB2D6 = 0b01011100;
	tRegAddr TXB2D7 = 0b01011101;
	tRegAddr RXB0CTRL = 0b01100000;
	tRegAddr RXB0SIDH = 0b01100001;
	tRegAddr RXB0SIDL = 0b01100010;
	tRegAddr RXB0EIDB = 0b01100011;
	tRegAddr RXB0EID0 = 0b01100100;
	tRegAddr RXB0DLC = 0b01100101;
	tRegAddr RXB0D0 = 0b01100110;
	tRegAddr RXB0D1 = 0b01100111;
	tRegAddr RXB0D2 = 0b01101000;
	tRegAddr RXB0D3 = 0b01101001;
	tRegAddr RXB0D4 = 0b01101010;
	tRegAddr RXB0D5 = 0b01101011;
	tRegAddr RXB0D6 = 0b01101100;
	tRegAddr RXB0D7 = 0b01101101;
	tRegAddr RXB1CTRL = 0b01110000;
	tRegAddr RXB1SIDH = 0b01110001;
	tRegAddr RXB1SIDL = 0b01110010;
	tRegAddr RXB1EIDB = 0b01110011;
	tRegAddr RXB1EID0 = 0b01110100;
	tRegAddr RXB1DLC = 0b01110101;
	tRegAddr RXB1D0 = 0b01110110;
	tRegAddr RXB1D1 = 0b01110111;
	tRegAddr RXB1D2 = 0b01111000;
	tRegAddr RXB1D3 = 0b01111001;
	tRegAddr RXB1D4 = 0b01111010;
	tRegAddr RXB1D5 = 0b01111011;
	tRegAddr RXB1D6 = 0b01111100;
	tRegAddr RXB1D7 = 0b01111101;
	tRegAddr CNF3 =0x28;
	tRegAddr CNF2 =0x29;
	tRegAddr CNF1 =0x2A;
	/*
	* *****************************************************
	* end MCP2515 Registers
	*/
	/*
	* *****************************************************
	* MASK bytes follow
	*/
	// BFPCTRL
	tMask B1BFS = 0b00100000;
	tMask B0BFS = 0b00010000;
	tMask B1BFE = 0b00001000;
	tMask B0BFE = 0b00000100;
	tMask B1BFM = 0b00000010;
	tMask B0BFM = 0b00000001;
	// TXRTSCTRL
	tMask B2RTS = 0b00100000;
	tMask B1RTS = 0b00010000;
	tMask B0RTS = 0b00001000;
	tMask B2RTSM = 0b00000100;
	tMask B1RTSM = 0b00000010;
	tMask B0RTSM = 0b00000001;
	// CANSTAT
	tMask OPMOD2 = 0b10000000;
	tMask OPMOD1 = 0b01000000;
	tMask OPMOD0 = 0b00100000;
	tMask ICOD2 = 0b00001000;
	tMask ICOD1 = 0b00000100;
	tMask ICOD0 = 0b00000010;
	// CANCTRL
	tMask REQOP2 = 0b10000000;
	tMask REQOP1 = 0b01000000;
	tMask REQOP0 = 0b00100000;
	tMask ABAT = 0b00010000;
	tMask OSM = 0b00001000;
	tMask CLKEN = 0b00000100;
	tMask CLKPRE1 = 0b00000010;
	tMask CLKPRE0 = 0b00000001;
	// CNF3
	tMask SOF = 0b10000000;
	tMask WAKFIL = 0b01000000;
	tMask PHSEG22 = 0b00000100;
	tMask PHSEG21 = 0b00000010;
	tMask PHSEG20 = 0b00000001;
	// CANF2
	tMask BTLMODE = 0b10000000;
	tMask SAM = 0b01000000;
	tMask PHSEG12 = 0b00100000;
	tMask PHSEG11 = 0b00010000;
	tMask PHSEG10 = 0b00001000;
	tMask PHSEG2 = 0b00000100;
	tMask PHSEG1 = 0b00000010;
	tMask PHSEG0 = 0b00000001;
	// CANF1
	tMask SJW1 = 0b10000000;
	tMask SJW0 = 0b01000000;
	tMask BRP5 = 0b00100000;
	tMask BRP4 = 0b00010000;
	tMask BRP3 = 0b00001000;
	tMask BRP2 = 0b00000100;
	tMask BRP1 = 0b00000010;
	tMask BRP0 = 0b00000001;
	// CANINTE
	tMask MERRE = 0b10000000;
	tMask WAKIE = 0b01000000;
	tMask ERRIE = 0b00100000;
	tMask TX2IE = 0b00010000;
	tMask TX1IE = 0b00001000;
	tMask TX0IE = 0b00000100;
	tMask RX1IE = 0b00000010;
	tMask RX0IE = 0b00000001;
	// CANINTF
	tMask MERRF = 0b10000000;
	tMask WAKIF = 0b01000000;
	tMask ERRIF = 0b00100000;
	tMask TX2IF = 0b00010000;
	tMask TX1IF = 0b00001000;
	tMask TX0IF = 0b00000100;
	tMask RX1IF = 0b00000010;
	tMask RX0IF = 0b00000001;
	// EFLG
	tMask RX1OVR = 0b10000000;
	tMask RX0OVR = 0b01000000;
	tMask TXBO = 0b00100000;
	tMask TXEP = 0b00010000;
	tMask RXEP = 0b00001000;
	tMask TXWAR = 0b00000100;
	tMask RXWAR = 0b00000010;
	tMask EWARN = 0b00000001;
	// TXB0CTRL, TXB1CTRL, TXB2CTRL,
	tMask ABTF = 0b01000000;
	tMask MLOA = 0b00100000;
	tMask TXERR = 0b00010000;
	tMask TXREQ = 0b00001000;
	tMask TXP1 = 0b00000010;
	tMask TXP0 = 0b00000001;
	// RXB0CTRL
	tMask RXM1 = 0b01000000;
	tMask RXM0 = 0b00100000;
	tMask RXRTR = 0b00001000;
	tMask BUKT = 0b00000100;
	tMask BUKT1 = 0b00000010;
	tMask FILHIT0 = 0b00000001;
	// RXB1CTRL
	tMask FILHIT2 = 0b00000100;
	tMask FILHIT1 = 0b00000010;
	//other bit masks - these are not settable using BitModift - hence different type
	//TXBnSIDH
	tBitMask SID10 = 0b10000000;
	tBitMask SID9 = 0b01000000;
	tBitMask SID8 = 0b00100000;
	tBitMask SID7 = 0b00010000;
	tBitMask SID6 = 0b00001000;
	tBitMask SID5 = 0b10000100;
	tBitMask SID4 = 0b10000010;
	tBitMask SID3 = 0b10000001;
	//TXBnSIDL
	tBitMask SID2 = 0b10000000;
	tBitMask SID1 = 0b01000000;
	tBitMask SID0 = 0b00100000;
	tBitMask EXIDE = 0b00001000;
	tBitMask EID17 = 0b00000010;
	tBitMask EID16 = 0b00000001;
	//TXBnDLC
	tBitMask RTR = 0b01000000;
	tBitMask DLC3 = 0b00001000;
	tBitMask DLC2 = 0b10000100;
	tBitMask DLC1 = 0b10000010;
	tBitMask DLC0 = 0b10000001;
	/*
	* *****************************************************
	* INSTRUCTION constants follow - see datasheet section describing SPI Intruction Set
	*/
	tIns DONT_CARE = 0b11111111;
	tIns RESET_INS = 0b11000000; // MCP2515 reset instruction
	tIns READ_INS = 0b00000011; // MCP2515 read data from register beginning at selected address
	tIns READ_RXB0SIDH_INS = 0b10010000; // Receive Buffer 0. Start at RXB0SIDH(61h)= 8 MSBs of the received msg identifier
	tIns READ_RXB0D0_INS = 0b10010010; // Receive Buffer 0. Start at RXB0D0(66h) = Byte0 of eight possible message bytes
	tIns READ_RXB1SIDH_INS = 0b10010100; // Receive Buffer 1. Start at RXB0SIDH(71h)= 8 MSBs of the received msg identifier
	tIns READ_RXB1D0_D0_INS = 0b10010110; // Receive Buffer 1. Start at RXB0D0(76h) = Byte0 of eight possible message bytes
	tIns WRITE_INS = 0b00000010; // Write data at selected address
	tIns LD_TXB0SIDH_INS = 0b01000000; // Load TX Buffer 0, Start at address TXB0SIDH(31h)
	tIns LD_TXB0D0_INS = 0b01000001;
	tIns LD_TXB1SIDH_INS = 0b01000010;
	tIns LD_TXB1D0_INS = 0b01000011;
	tIns LD_TXB2SIDH_INS = 0b01000100;
	tIns LD_TXB2D0_INS = 0b01000101;
	tIns RTS_T0_INS = 0b10000001;
	tIns RTS_T1_INS = 0b10000010;
	tIns RTS_T2_INS = 0b10000100;
	tIns RTS_T0T1_INS = 0b10000011;
	tIns RTS_T0T2_INS = 0b10000101;
	tIns RTS_T1T2_INS = 0b10000110;
	tIns RTS_T0T1T2_INS = 0b10000111;
	tIns READ_STATUS_INS = 0b10100000;
	tIns RX_STATUS_INS = 0b10110000;
	tIns BIT_MODIFY_INS = 0b00000101;
	/*
	* *****************************************************
	* end INSTRUCTION constants definitions
	*/
	/*
	***************************************
	*/

The second file ...

	* Voltage Bias - the blog * Gilbert Waltoon
	*
	* Released under a GNU General Public License v3.0
	*
	* FILENAME : MCP2515_Registers.cpp
	* PURPOSE : UTILITIES FOR MCP2515 CAN CONTROLLER
	*
	*
	* VERSION 0
	*
	*
	*/
	#include "Arduino.h"
	#include "SPI.h"
	#include "MCP2515_Registers.h"
	//Reset the MCP2515
	void resetIns(){
	digitalWrite(chipSelectPin, LOW);
	SPI.transfer(RESET_INS);
	delay(100);
	digitalWrite(chipSelectPin, HIGH);
	return;
	}
	// Returns the value in the register addr
	byte readIns(tRegAddr addr){
	byte dataOut;
	digitalWrite(chipSelectPin, LOW);
	SPI.transfer((byte)READ_INS);
	SPI.transfer((byte)addr);
	dataOut = SPI.transfer((byte)DONT_CARE);
	digitalWrite(chipSelectPin, HIGH);
	return dataOut;
	}
	//Fast read of MCP2515 RX buffer. Returns value read.
	//Possible arguments are READ_RXB0SIDH_INS, READ_RXB0D0_INS, READ_RXB1SIDH_INS, READ_RXB0D0_INS,
	byte readRxBuffIns(tIns ins){
	byte dataOut;
	digitalWrite(chipSelectPin, LOW);
	SPI.transfer((byte)ins);
	dataOut = SPI.transfer((byte)DONT_CARE);
	digitalWrite(chipSelectPin, HIGH);
	return dataOut;
	}
	//Write 'byte' to MCP2515 register 'tRegAddr'
	void writeIns(tRegAddr addr, byte dataIn){
	digitalWrite(chipSelectPin, LOW);
	SPI.transfer((byte)WRITE_INS);
	SPI.transfer((byte)addr);
	SPI.transfer(dataIn);
	digitalWrite(chipSelectPin, HIGH);
	return;
	}
	//Fast write of dataIn to the MCP2515 TX buffer.
	//Possible tIns arguments are LD_TXB0SIDH_INS, LD_TXB0D0_INS, LD_TXB1SIDH_INS, LD_TXB1D0_INS, LD_TXB2SIDH_INS LD_TXB2D0_INS
	void ldTxBuffIns(tIns ins, byte dataIn){
	digitalWrite(chipSelectPin, LOW);
	SPI.transfer((byte)ins);
	SPI.transfer(dataIn);
	digitalWrite(chipSelectPin, HIGH);
	return;
	}
	//Request MCP2515 to send the message sitting in trasmit-buffer 'tIns'.
	void rqstToSendIns(tIns ins){
	digitalWrite(chipSelectPin, LOW);
	SPI.transfer((byte)ins);
	digitalWrite(chipSelectPin, HIGH);
	return;
	}
	//Modify register bits. 1st argument is register. 2nd argument is the bits to modify. 3rd argument is new bit values to write.
	void bitModifyIns(tRegAddr addr, tMask mask, tMask setBits){
	digitalWrite(chipSelectPin, LOW);
	SPI.transfer((byte)BIT_MODIFY_INS);
	SPI.transfer((byte)addr);
	SPI.transfer((byte)mask);
	SPI.transfer((byte)setBits);
	digitalWrite(chipSelectPin, HIGH);
	return;
	}
	//Fast access to selected register bits.
	byte readStatusIns(){
	byte dataOut;
	digitalWrite(chipSelectPin, LOW);
	SPI.transfer((byte)READ_STATUS_INS);
	dataOut=SPI.transfer((byte)DONT_CARE);
	digitalWrite(chipSelectPin, HIGH);
	return dataOut;
	}
	// Fast access to status information on messages received.
	byte rxStatusIns(){
	byte dataOut;
	digitalWrite(chipSelectPin, LOW);
	SPI.transfer((byte)RX_STATUS_INS);
	dataOut=SPI.transfer((byte)DONT_CARE);
	digitalWrite(chipSelectPin, HIGH);
	return dataOut;
	}
	//Print list of CAN errors on serial port. Returns TRUE is errors occurred.
	bool check4Errs(){
	// read error flag register and print out any errors
	// return false if no errors
	byte eFlgByte;
	eFlgByte = readIns(EFLG);
	if(eFlgByte) {
	Serial.println("!!!!!!!!!!! Error reported by EFLG register !!!!!!!!!!!!");
	if(eFlgByte & EWARN) Serial.println("EWARN WAS SET: >=96 errors in TEC or REC");
	if(eFlgByte & RXWAR) Serial.println("RXWAR WAS SET: >=96 errors in REC");
	if(eFlgByte & TXWAR) Serial.println("TXWAR WAS SET: >=96 errors in TEC");
	if(eFlgByte & RXEP) Serial.println("RXEP WAS SET: >=128 errors in REC");
	if(eFlgByte & TXEP) Serial.println("TXEP WAS SET: >=128 errors in REC");
	if(eFlgByte & TXBO) Serial.println("TXBO WAS SET: TEC reached 255; BUS OFF");
	if(eFlgByte & RX0OVR) Serial.println("RX0OVR WAS SET: RECEIVE BUFFER_0 OVERFLOWED");
	if(eFlgByte & RX1OVR) Serial.println("RX1OVR WAS SET: RECEIVE BUFFER_1 OVERFLOWED");
	Serial.print("TX ERROR COUNT="); Serial.print("\t"); Serial.println( readIns(TEC) );
	Serial.print("RX ERROR COUNT="); Serial.print("\t"); Serial.println( readIns(REC) );
	Serial.println("!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!");
	Serial.println( );
	return true;
	}
	Serial.println( "No errors");
	return false;
	}
	//Select MCP2515 mode. Possible arguments are "Normal" "Sleep" "Loopback" "Listen" "Configuration". Returns TRUE if successful.
	bool setMode(String szMode){
	if
	(szMode == "Normal") {
	bitModifyIns(CANCTRL, REQOP2|REQOP1|REQOP0, 0);
	Serial.println("Entering mode: NORMAL");
	return true;
	}
	else if
	(szMode == "Sleep") {
	bitModifyIns(CANCTRL, REQOP2|REQOP1|REQOP0, REQOP0);
	Serial.println("Entering mode: SLEEP");
	return true;
	}
	else if
	(szMode == "Loopback") {
	bitModifyIns(CANCTRL, REQOP2|REQOP1|REQOP0, REQOP1);
	Serial.println("Entering mode: LOOPBACK");
	return true;
	}
	else if
	(szMode == "Listen") {
	bitModifyIns(CANCTRL, REQOP2|REQOP1|REQOP0, REQOP1|REQOP0);
	Serial.println("Entering mode: LISTEN");
	return true;
	}
	else if
	(szMode == "Configuration"){
	bitModifyIns(CANCTRL, REQOP2|REQOP1|REQOP0, REQOP1|REQOP2);
	Serial.println("Entering mode: CONFIGURATION");
	return true;
	}
	else {
	Serial.println ("Mode wasn't recognised in call to function setMode(mode)");
	return false;
	}
	}