`define load_inst		4'd0
`define store_inst		4'd1
`define alu_inst		4'd2
`define control_transfer_inst	4'd3

`define ACCn		2'd0
`define Xn		2'd1
`define Sn		2'd2
`define PCn		2'd3

`define Never		4'd0
`define Always		4'd1
`define Zequal0		4'd2
`define Zequal1		4'd3

`define FnReg		4'd0
`define FnNOT		4'd1
`define FnLSL		4'd2
`define FnLSR		4'd3
`define FnADD		4'd4
`define FnSUB		4'd5
`define FnAND		4'd6
`define FnOR		4'd7
`define FnMem		4'd8

`define NOP		{`load_inst,`ACCn,`ACCn,`FnReg}
`define LDA		{`load_inst,`ACCn,`ACCn,`FnMem}
`define LDX		{`load_inst,`ACCn,`Xn,`FnMem}
`define LDS		{`load_inst,`ACCn,`Sn,`FnMem}
`define STA		{`store_inst,`ACCn,`ACCn,`FnReg}
`define STX		{`store_inst,`Xn,`Xn,`FnReg}
`define STS		{`store_inst,`Sn,`Sn,`FnReg}
`define ADD		{`alu_inst,`ACCn,`ACCn,`FnADD}
`define SUB		{`alu_inst,`ACCn,`ACCn,`FnSUB}
`define AND		{`alu_inst,`ACCn,`ACCn,`FnAND}
`define OR		{`alu_inst,`ACCn,`ACCn,`FnOR}
`define COM		{`alu_inst,`ACCn,`ACCn,`FnNOT}
`define LSL		{`alu_inst,`ACCn,`ACCn,`FnLSL}
`define LSR		{`alu_inst,`ACCn,`ACCn,`FnLSR}
`define BA		{`control_transfer_inst,`PCn,`PCn,`Always}
`define BEQ		{`control_transfer_inst,`PCn,`PCn,`Zequal1}
`define BNE		{`control_transfer_inst,`PCn,`PCn,`Zequal0}

`define INHERENT	4'd0
`define PC_RELATIVE	4'd1
`define IMMEDIATE	4'd2
`define DIRECT		4'd3
`define INDEXED		4'd4