What is this in define variable line

Using Arduino Programming Questions
1

I found this in a library .h file for the Linear Technologies DAC LT2664:

does anyone know what the 4 digit/character underlined is? is the 'x' significant?

Thanks

Justin

#define LTC2664_CMD_WRITE_N 0x00 //!< Write to input register n
#define LTC2664_CMD_UPDATE_N 0x10 //!< Update (power up) DAC register n
#define LTC2664_CMD_WRITE_N_UPDATE_ALL 0x20 //!< Write to input register n, update (power-up) all
#define LTC2664_CMD_WRITE_N_UPDATE_N 0x30 //!< Write to input register n, update (power-up)
#define LTC2664_CMD_POWER_DOWN_N 0x40 //!< Power down n
#define LTC2664_CMD_POWER_DOWN_ALL 0x50 //!< Power down chip (all DAC's, MUX and reference)

#define LTC2664_CMD_SPAN 0x60 //!< Write span to dac n
#define LTC2664_CMD_CONFIG 0x70 //!< Configure reference / toggle
#define LTC2664_CMD_WRITE_ALL 0x80 //!< Write to all input registers
#define LTC2664_CMD_UPDATE_ALL 0x90 //!< Update all DACs
#define LTC2664_CMD_WRITE_ALL_UPDATE_ALL 0xA0 //!< Write to all input reg, update all DACs
#define LTC2664_CMD_MUX 0xB0 //!< Select MUX channel (controlled by 5 LSbs in data word)
#define LTC2664_CMD_TOGGLE_SEL 0xC0 //!< Select which DACs can be toggled (via toggle pin or global toggle bit)
#define LTC2664_CMD_GLOBAL_TOGGLE 0xD0 //!< Software toggle control via global toggle bit
#define LTC2664_CMD_SPAN_ALL 0xE0 //!< Set span for all DACs
#define LTC2664_CMD_NO_OPERATION 0xF0 //!< No operation

2

0x00 is the Hex representation of zero

The 0x prefix indicates that the value is represented in Hex

3

Hello,

Maybe this file can help you with something:

C Programming for Arduino

4

Zero is zero. 0x00 could be written as 0 but looks better when used with 0x10, 0x20, etc.
The x is significant because 0x tells us that the following digits are to be interpreted as hexadecimal.

5

One of the first steps when compiling is a pre-compile step. One of the things that happens in that step is that everywhere where e.g. LTC2664_CMD_WRITE_N occurs in your code or the library, it is replaced by the value that is defined (0x00). The same for the other #defines that you showed.