User Manual

MCP Series

Brushed DC Motor Controllers

MCP Series User Manual

2.2.9 Handling values larger than a byte

Many Packet Serial commands require values larger than a byte can hold. In order to send or

receive those values they need to be broken up into 2 or more bytes. There are two ways this

can be done, high byte rst or low byte rst. Roboclaw expects the high byte rst. All command

arguments and values are either single bytes, words (2 bytes) or longs (4 bytes). All arguments

and values are integers (signed or unsigned). No oating point values (numbers with decimal

places) are used in Packet Serial commands.

To convert a 32bit value into 4 bytes you just need to shift the bits around:

unsigned char byte3 = MyLongValue>>24; //High byte

unsigned char byte2 = MyLongValue>>16;

unsigned char byte1 = MyLongValue>>8;

unsigned char byte0 = MyLongValue; //Low byte

The same applies to 16bit values:

unsigned char byte1 = MyWordValue>>8; //High byte

unsigned char byte0 = MyWordValue; //Low byte

The oposite can also be done. Convert several bytes into a 16bit or 32bit value:

unsigned long MyLongValue = byte3<<24 | byte2<<16 | byte1<<8 | byte0;

unsigned int MyWordValue = byte1<<8 | byte0;

Packet Serial commands, when a value must be broken into multiple bytes or combined from

multiple bytes it will be indicated either by (2 bytes) or (4 bytes).