Command Set¶

Command IDs¶

The following table shows the available commands of the USBoard-USS5.

Command	Value	Description
`CMD_CONNECT`	0	Check connection
`CMD_SET_CHANNEL_ACTIVE`	1	Activate channel for sending / receiving
`CMD_GET_DATA_1TO8`	2	Request data of sensors 1 to 8
`CMD_GET_DATA_9TO16`	3	Request data of sensors 9 to 16
`CMD_WRITE_PARASET`	4	Upload parameter set to board (volatile)
`CMD_WRITE_PARASET_TO_EEPROM`	5	Write parameter set to board’s EEPROM (non-volatile)
`CMD_READ_PARASET`	6	Read current parameter set
`CMD_GET_ANALOGIN`	7	Read values of analogue inputs
–	8-12	Reserved
`CMD_GET_DATA`	13	Request data of all sensors

CAN Communication¶

The default base address is 0x400. This base address can be changed in the parameter set.

The addresses used by the USBoard-USS5 are calculated from the base address by adding the following offsets.

Offset to base address	Function
`+0`	Receive commands
`+1`	Answer to `CMD_CONNECT`
`+2`	First answer to `CMD_GET_DATA_1TO8`
`+3`	Second answer to `CMD_GET_DATA_1TO8`
`+4`	First answer to `CMD_GET_DATA_9TO16`
`+5`	2nd answer to `CMD_GET_DATA_9TO16`
`+6`	Answer to `CMD_READ_PARASET`
`+7`	Answer to `CMD_GET_ANALOGIN`
`+8`	Answer to `CMD_WRITE_PARASET`
`+9`	Answer to `CMD_WRITE_PARASET_TO_EEPROM`
`+13`	1st Answer to `CMD_GET_DATA` (group 0: 1 to 4)
`+14`	2nd Answer to `CMD_GET_DATA` (group 1: 5 to 8)
`+15`	3rd Answer to `CMD_GET_DATA` (group 2: 9 to 12)
`+16`	4th Answer to `CMD_GET_DATA` (group 3: 13 to 16)

USB / Serial Interface¶

Communication via USB is done via a USB-serial-converter on the USBoard-USS5. The computer’s operating system can access it like a traditional serial interface. On request the USB converter can be replaced by an RS-232 transmitter. This does not affect the communication protocol of the serial interface.

Note

The RS-232 interface requires a common ground connection between the USBoard-USS5 and the computer.

The serial interface runs at 19200 Baud. Its protocol has the same format as the CAN communication except for the following addition:

Every message from the USBoard-USS5 begins with a start byte which must have the value 0xFF. After each message, made up of eight data bytes, a 16 bit checksum is sent. Because of this, a complete message is 11 bytes long.

Byte 1	Bytes 2-9	Byte 10	Byte 11
`0xFF`	data bytes	checksum high byte	checksum low byte

The checksum is calculated with an CRC-CCITT algorithm using 8 databytes.

Messages to the USBoard-USS5 only contain the data bytes.

Example implementation of the checksum calulation (C code):

unsigned int getCheckSum(unsigned char *c, size_t iNumBytes){
	unsigned int uCrc16;
	unsigned char ucData[2];
	size_t i;

	uCrc16 = 0;
	ucData[0] = 0;
	for(i=0; i<iNumBytes; i++){
		ucData[1] = ucData[0];
		ucData[0] = c[i];

		if(uCrc16 & 0x8000){
			uCrc16 = (uCrc16 & 0x7fff) << 1;
			uCrc16^= 0x1021;
		}else{
			uCrc16 <<= 1;
		}
		uCrc16^= (unsigned int)(ucData[0]) | ((unsigned int)(ucData[1]) << 8);
	}

	return uCrc16;
}