ABOUT reg.h

#ifndef __ALTERA_AVALON_LCD_16207_REGS_H__# define __ALTERA_AVALON_LCD_16207_REGS_H__

/*

///////////////////////////////////////////////////////////////////////////

//

// ALTERA_AVALON_LCD_16207 PERIPHERAL

//

// Provides a hardware interface that allows software to

// access the two (2) internal 8-bit registers in an Optrex

// model 16207 (or equivalent) character LCD display (the kind

// shipped with the Nios Development Kit, 2 rows x 16 columns).

//

// Because the interface to the LCD module is "not quite Avalon,"

// the hardware in this module ends-up mapping the module's

// two physical read-write registers into four Avalon-visible

// registers: Two read-only registers and two write-only registers.

// A picture is worth a thousand words:

//

// THE REGISTER MAP

//

// 7 6 5 4 3 2 1 0 Offset

// +-----+-----+-----+-----+-----+-----+-----+-----+

// RS = 0 | Command Register (WRITE-Only) | 0

// +-----+-----+-----+-----+-----+-----+-----+-----+

// RS = 0 | Status Register (READ -Only) | 1

// +-----+-----+-----+-----+-----+-----+-----+-----+

// RS = 1 | Data Register (WRITE-Only) | 2

// +-----+-----+-----+-----+-----+-----+-----+-----+

// RS = 1 | Data Register (READ -Only) | 3

// +-----+-----+-----+-----+-----+-----+-----+-----+

//

///////////////////////////////////////////////////////////////////////////

*/

# include <io.h>

# define IOADDR_ALTERA_AVALON_LCD_16207_COMMAND(base) __IO_CALC_ADDRESS_NATIVE(base, 0)# define IOWR_ALTERA_AVALON_LCD_16207_COMMAND(base, data) IOWR(base, 0, data)

# define IOADDR_ALTERA_AVALON_LCD_16207_STATUS(base) __IO_CALC_ADDRESS_NATIVE(base, 1)# define IORD_ALTERA_AVALON_LCD_16207_STATUS(base) IORD(base, 1)

# define ALTERA_AVALON_LCD_16207_STATUS_BUSY_MSK (0x00000080u)# define ALTERA_AVALON_LCD_16207_STATUS_BUSY_OFST (7)

# define IOADDR_ALTERA_AVALON_LCD_16207_DATA_WR(base) __IO_CALC_ADDRESS_NATIVE(base, 2)# define IOWR_ALTERA_AVALON_LCD_16207_DATA(base, data) IOWR(base, 2, data)

# define IOADDR_ALTERA_AVALON_LCD_16207_DATA_RD(base) __IO_CALC_ADDRESS_NATIVE(base, 3)# define IORD_ALTERA_AVALON_LCD_16207_DATA(base) IORD(base, 3)

# endif

who can tell me why the Command Register Offset is 0,Status Register offset is 1

and the other register offset 1,2