| Line 66... |
Line 66... |
output reg [7:0] alu_x;
|
output reg [7:0] alu_x;
|
output reg [7:0] alu_y;
|
output reg [7:0] alu_y;
|
|
|
reg [7:0] A;
|
reg [7:0] A;
|
reg [7:0] STATUS;
|
reg [7:0] STATUS;
|
reg [7:0] result;
|
reg [9:0] result;
|
reg [7:0] op1;
|
reg [7:0] op1;
|
reg [7:0] op2;
|
reg [7:0] op2;
|
reg [7:0] bcdl;
|
reg [7:0] bcdl;
|
reg [7:0] bcdh;
|
reg [7:0] bcdh;
|
reg [7:0] bcdh2;
|
reg [7:0] bcdh2;
|
| Line 106... |
Line 106... |
EOR_IDY, LSR_ACC, ORA_IMM, ORA_ZPG, ORA_ZPX, ORA_ABS,
|
EOR_IDY, LSR_ACC, ORA_IMM, ORA_ZPG, ORA_ZPX, ORA_ABS,
|
ORA_ABX, ORA_ABY, ORA_IDX, ORA_IDY, ROL_ACC, ROR_ACC,
|
ORA_ABX, ORA_ABY, ORA_IDX, ORA_IDY, ROL_ACC, ROR_ACC,
|
SBC_IMM, SBC_ZPG, SBC_ZPX, SBC_ABS, SBC_ABX, SBC_ABY,
|
SBC_IMM, SBC_ZPG, SBC_ZPX, SBC_ABS, SBC_ABX, SBC_ABY,
|
SBC_IDX, SBC_IDY, LDA_IMM, LDA_ZPG, LDA_ZPX, LDA_ABS,
|
SBC_IDX, SBC_IDY, LDA_IMM, LDA_ZPG, LDA_ZPX, LDA_ABS,
|
LDA_ABX, LDA_ABY, LDA_IDX, LDA_IDY, PLA_IMP : begin
|
LDA_ABX, LDA_ABY, LDA_IDX, LDA_IDY, PLA_IMP : begin
|
A <= result;
|
A <= result[7:0];
|
alu_result <= result;
|
alu_result <= result[7:0];
|
alu_status <= STATUS;
|
alu_status <= STATUS;
|
end
|
end
|
LDX_IMM, LDX_ZPG, LDX_ZPY, LDX_ABS, LDX_ABY, TAX_IMP,
|
LDX_IMM, LDX_ZPG, LDX_ZPY, LDX_ABS, LDX_ABY, TAX_IMP,
|
TSX_IMP, INX_IMP, DEX_IMP : begin
|
TSX_IMP, INX_IMP, DEX_IMP : begin
|
alu_x <= result;
|
alu_x <= result[7:0];
|
alu_status <= STATUS;
|
alu_status <= STATUS;
|
end
|
end
|
TXS_IMP : begin
|
TXS_IMP : begin
|
alu_x <= result;
|
alu_x <= result[7:0];
|
end
|
end
|
TXA_IMP, TYA_IMP : begin
|
TXA_IMP, TYA_IMP : begin
|
A <= result;
|
A <= result[7:0];
|
alu_status <= STATUS;
|
alu_status <= STATUS;
|
end
|
end
|
LDY_IMM, LDY_ZPG, LDY_ZPX, LDY_ABS, LDY_ABX, TAY_IMP,
|
LDY_IMM, LDY_ZPG, LDY_ZPX, LDY_ABS, LDY_ABX, TAY_IMP,
|
INY_IMP, DEY_IMP : begin
|
INY_IMP, DEY_IMP : begin
|
alu_y <= result;
|
alu_y <= result[7:0];
|
alu_status <= STATUS;
|
alu_status <= STATUS;
|
end
|
end
|
CMP_IMM, CMP_ZPG, CMP_ZPX, CMP_ABS, CMP_ABX, CMP_ABY,
|
CMP_IMM, CMP_ZPG, CMP_ZPX, CMP_ABS, CMP_ABX, CMP_ABY,
|
CMP_IDX, CMP_IDY, CPX_IMM, CPX_ZPG, CPX_ABS, CPY_IMM,
|
CMP_IDX, CMP_IDY, CPX_IMM, CPX_ZPG, CPX_ABS, CPY_IMM,
|
CPY_ZPG, CPY_ABS : begin
|
CPY_ZPG, CPY_ABS : begin
|
alu_status <= STATUS;
|
alu_status <= STATUS;
|
end
|
end
|
PHA_IMP, STA_ZPG, STA_ZPX, STA_ABS, STA_ABX, STA_ABY,
|
PHA_IMP, STA_ZPG, STA_ZPX, STA_ABS, STA_ABX, STA_ABY,
|
STA_IDX, STA_IDY : begin
|
STA_IDX, STA_IDY : begin
|
alu_result <= result;
|
alu_result <= result[7:0];
|
end
|
end
|
STX_ZPG, STX_ZPY, STX_ABS : begin
|
STX_ZPG, STX_ZPY, STX_ABS : begin
|
alu_x <= result;
|
alu_x <= result[7:0];
|
end
|
end
|
STY_ZPG, STY_ZPX, STY_ABS : begin
|
STY_ZPG, STY_ZPX, STY_ABS : begin
|
alu_y <= result;
|
alu_y <= result[7:0];
|
end
|
end
|
SEC_IMP : begin
|
SEC_IMP : begin
|
alu_status[C] <= 1;
|
alu_status[C] <= 1;
|
end
|
end
|
SED_IMP : begin
|
SED_IMP : begin
|
| Line 186... |
Line 186... |
INC_ZPG, INC_ZPX, INC_ABS, INC_ABX, DEC_ZPG, DEC_ZPX,
|
INC_ZPG, INC_ZPX, INC_ABS, INC_ABX, DEC_ZPG, DEC_ZPX,
|
DEC_ABS, DEC_ABX, ASL_ZPG, ASL_ZPX, ASL_ABS, ASL_ABX,
|
DEC_ABS, DEC_ABX, ASL_ZPG, ASL_ZPX, ASL_ABS, ASL_ABX,
|
LSR_ZPG, LSR_ZPX, LSR_ABS, LSR_ABX, ROL_ZPG, ROL_ZPX,
|
LSR_ZPG, LSR_ZPX, LSR_ABS, LSR_ABX, ROL_ZPG, ROL_ZPX,
|
ROL_ABS, ROL_ABX, ROR_ZPG, ROR_ZPX, ROR_ABS, ROR_ABX :
|
ROL_ABS, ROL_ABX, ROR_ZPG, ROR_ZPX, ROR_ABS, ROR_ABX :
|
begin
|
begin
|
alu_result <= result;
|
alu_result <= result[7:0];
|
alu_status <= STATUS;
|
alu_status <= STATUS;
|
end
|
end
|
default : begin
|
default : begin
|
end
|
end
|
endcase
|
endcase
|
| Line 199... |
Line 199... |
|
|
always @ (*) begin
|
always @ (*) begin
|
if (alu_enable == 1) begin
|
if (alu_enable == 1) begin
|
op1 = A;
|
op1 = A;
|
op2 = alu_a;
|
op2 = alu_a;
|
result = A;
|
result = A[7:0];
|
|
result[9:8] = 0;
|
STATUS[N] = alu_status[N];
|
STATUS[N] = alu_status[N];
|
STATUS[C] = alu_status[C];
|
STATUS[C] = alu_status[C];
|
STATUS[V] = alu_status[V];
|
STATUS[V] = alu_status[V];
|
STATUS[B] = alu_status[B];
|
STATUS[B] = alu_status[B];
|
STATUS[I] = alu_status[I];
|
STATUS[I] = alu_status[I];
|
| Line 219... |
Line 220... |
sign = op2[7];
|
sign = op2[7];
|
|
|
case (alu_opcode)
|
case (alu_opcode)
|
// BIT - Bit Test
|
// BIT - Bit Test
|
BIT_ZPG, BIT_ABS: begin
|
BIT_ZPG, BIT_ABS: begin
|
result = A & alu_a;
|
result[7:0] = A & alu_a;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// PLA - Pull Accumulator
|
// PLA - Pull Accumulator
|
PLA_IMP : begin
|
PLA_IMP : begin
|
result = alu_a;
|
result[7:0] = alu_a;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// TAX - Transfer Accumulator to X
|
// TAX - Transfer Accumulator to X
|
// TAY - Transfer Accumulator to Y
|
// TAY - Transfer Accumulator to Y
|
// PHA - Push Accumulator
|
// PHA - Push Accumulator
|
// STA - Store Accumulator
|
// STA - Store Accumulator
|
TAX_IMP, TAY_IMP, PHA_IMP, STA_ZPG, STA_ZPX, STA_ABS, STA_ABX,
|
TAX_IMP, TAY_IMP, PHA_IMP, STA_ZPG, STA_ZPX, STA_ABS, STA_ABX,
|
STA_ABY, STA_IDX, STA_IDY : begin
|
STA_ABY, STA_IDX, STA_IDY : begin
|
result = A;
|
result[7:0] = A;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// STX - Store X Register
|
// STX - Store X Register
|
// TXA - Transfer X to Accumulator
|
// TXA - Transfer X to Accumulator
|
// TXS - Transfer X to Stack pointer
|
// TXS - Transfer X to Stack pointer
|
STX_ZPG, STX_ZPY, STX_ABS, TXA_IMP, TXS_IMP : begin
|
STX_ZPG, STX_ZPY, STX_ABS, TXA_IMP, TXS_IMP : begin
|
result = alu_x;
|
result[7:0] = alu_x;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// STY - Store Y Register
|
// STY - Store Y Register
|
// TYA - Transfer Y to Accumulator
|
// TYA - Transfer Y to Accumulator
|
STY_ZPG, STY_ZPX, STY_ABS, TYA_IMP : begin
|
STY_ZPG, STY_ZPX, STY_ABS, TYA_IMP : begin
|
result = alu_y;
|
result[7:0] = alu_y;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// INC - Increment memory
|
// INC - Increment memory
|
INC_ZPG, INC_ZPX, INC_ABS, INC_ABX : begin
|
INC_ZPG, INC_ZPX, INC_ABS, INC_ABX : begin
|
result = alu_a + 1;
|
result[7:0] = alu_a + 1;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// INX - Increment X Register
|
// INX - Increment X Register
|
INX_IMP: begin
|
INX_IMP: begin
|
result = alu_x + 1;
|
result[7:0] = alu_x + 1;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// INY - Increment Y Register
|
// INY - Increment Y Register
|
INY_IMP : begin
|
INY_IMP : begin
|
result = alu_y + 1;
|
result[7:0] = alu_y + 1;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// DEC - Decrement memory
|
// DEC - Decrement memory
|
DEC_ZPG, DEC_ZPX, DEC_ABS, DEC_ABX : begin
|
DEC_ZPG, DEC_ZPX, DEC_ABS, DEC_ABX : begin
|
result = alu_a - 1;
|
result[7:0] = alu_a - 1;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// DEX - Decrement X register
|
// DEX - Decrement X register
|
DEX_IMP: begin
|
DEX_IMP: begin
|
result = alu_x - 1;
|
result[7:0] = alu_x - 1;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// DEY - Decrement Y Register
|
// DEY - Decrement Y Register
|
DEY_IMP: begin
|
DEY_IMP: begin
|
result = alu_y - 1;
|
result[7:0] = alu_y - 1;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// ADC - Add with carry
|
// ADC - Add with carry
|
ADC_IMM, ADC_ZPG, ADC_ZPX, ADC_ABS,
|
ADC_IMM, ADC_ZPG, ADC_ZPX, ADC_ABS,
|
ADC_ABX, ADC_ABY, ADC_IDX, ADC_IDY : begin
|
ADC_ABX, ADC_ABY, ADC_IDX, ADC_IDY : begin
|
if (!alu_status[D]) begin
|
if (!alu_status[D]) begin
|
{STATUS[C],result} = op1 + op2 + alu_status[C];
|
result = op1 + op2 + alu_status[C];
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[V] = ((op1[7] == op2[7]) && (op1[7] != result[7])) ? 1 : 0;
|
STATUS[V] = ((op1[7] == op2[7]) && (op1[7] != result[7])) ? 1 : 0;
|
|
STATUS[C] = result[8];
|
end
|
end
|
else begin
|
else begin
|
AL = op1[3:0] + op2[3:0] + alu_status[C];
|
AL = op1[3:0] + op2[3:0] + alu_status[C];
|
AH = op1[7:4] + op2[7:4];
|
AH = op1[7:4] + op2[7:4];
|
STATUS[Z] = (AL == 0 && AH == 0) ? 1 : 0;
|
STATUS[Z] = (AL == 0 && AH == 0) ? 1 : 0;
|
| Line 331... |
Line 333... |
end
|
end
|
else begin
|
else begin
|
bcdh2 = bcdh;
|
bcdh2 = bcdh;
|
end
|
end
|
STATUS[C] = bcdh2[4] || bcdh2[5];
|
STATUS[C] = bcdh2[4] || bcdh2[5];
|
result = {bcdh2[3:0],bcdl[3:0]};
|
result[7:0] = {bcdh2[3:0],bcdl[3:0]};
|
end
|
end
|
end
|
end
|
|
|
// AND - Logical AND
|
// AND - Logical AND
|
AND_IMM, AND_ZPG, AND_ZPX, AND_ABS, AND_ABX, AND_ABY, AND_IDX,
|
AND_IMM, AND_ZPG, AND_ZPX, AND_ABS, AND_ABX, AND_ABY, AND_IDX,
|
AND_IDY : begin
|
AND_IDY : begin
|
result = A & alu_a;
|
result[7:0] = A & alu_a;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// CMP - Compare
|
// CMP - Compare
|
CMP_IMM, CMP_ZPG, CMP_ZPX, CMP_ABS, CMP_ABX, CMP_ABY, CMP_IDX,
|
CMP_IMM, CMP_ZPG, CMP_ZPX, CMP_ABS, CMP_ABX, CMP_ABY, CMP_IDX,
|
CMP_IDY : begin
|
CMP_IDY : begin
|
result = A - alu_a;
|
result[7:0] = A - alu_a;
|
STATUS[C] = (A >= alu_a) ? 1 : 0;
|
STATUS[C] = (A >= alu_a) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// EOR - Exclusive OR
|
// EOR - Exclusive OR
|
EOR_IMM, EOR_ZPG, EOR_ZPX, EOR_ABS, EOR_ABX, EOR_ABY,
|
EOR_IMM, EOR_ZPG, EOR_ZPX, EOR_ABS, EOR_ABX, EOR_ABY,
|
EOR_IDX, EOR_IDY : begin
|
EOR_IDX, EOR_IDY : begin
|
result = A ^ alu_a;
|
result[7:0] = A ^ alu_a;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// LDA - Load Accumulator
|
// LDA - Load Accumulator
|
| Line 367... |
Line 369... |
// LDY - Load Y Register
|
// LDY - Load Y Register
|
// TSX - Transfer Stack Pointer to X
|
// TSX - Transfer Stack Pointer to X
|
LDA_IMM, LDA_ZPG, LDA_ZPX, LDA_ABS, LDA_ABX, LDA_ABY, LDA_IDX,
|
LDA_IMM, LDA_ZPG, LDA_ZPX, LDA_ABS, LDA_ABX, LDA_ABY, LDA_IDX,
|
LDA_IDY, LDX_IMM, LDX_ZPG, LDX_ZPY, LDX_ABS, LDX_ABY, LDY_IMM,
|
LDA_IDY, LDX_IMM, LDX_ZPG, LDX_ZPY, LDX_ABS, LDX_ABY, LDY_IMM,
|
LDY_ZPG, LDY_ZPX, LDY_ABS, LDY_ABX, TSX_IMP : begin
|
LDY_ZPG, LDY_ZPX, LDY_ABS, LDY_ABX, TSX_IMP : begin
|
result = alu_a;
|
result[7:0] = alu_a;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// ORA - Logical OR
|
// ORA - Logical OR
|
ORA_IMM, ORA_ZPG, ORA_ZPX, ORA_ABS, ORA_ABX, ORA_ABY, ORA_IDX,
|
ORA_IMM, ORA_ZPG, ORA_ZPX, ORA_ABS, ORA_ABX, ORA_ABY, ORA_IDX,
|
ORA_IDY : begin
|
ORA_IDY : begin
|
result = A | alu_a;
|
result[7:0] = A | alu_a;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// SBC - Subtract with Carry
|
// SBC - Subtract with Carry
|
SBC_IMM, SBC_ZPG, SBC_ZPX, SBC_ABS, SBC_ABX, SBC_ABY, SBC_IDX,
|
SBC_IMM, SBC_ZPG, SBC_ZPX, SBC_ABS, SBC_ABX, SBC_ABY, SBC_IDX,
|
SBC_IDY : begin
|
SBC_IDY : begin
|
result = op1 - op2 - (1 - alu_status[C]);
|
result = op1 - op2 - (1 - alu_status[C]);
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
STATUS[V] = ((op1[7] == op2[7]) && (op1[7] == result[7])) ? 1 : 0;
|
STATUS[V] = ((op1[7] ^ op2[7]) && (op1[7] ^ result[7])) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[C] = ~result[7];
|
STATUS[C] = ~(result[8] || result[9]);
|
if (alu_status[D]) begin
|
if (alu_status[D]) begin
|
AL = op1[3:0] - op2[3:0] - (1 - alu_status[C]);
|
AL = op1[3:0] - op2[3:0] - (1 - alu_status[C]);
|
AH = op1[7:4] - op2[7:4];
|
AH = op1[7:4] - op2[7:4];
|
if (AL[4]) begin
|
if (AL[4]) begin
|
bcdl = AL - 6;
|
bcdl = AL - 6;
|
| Line 405... |
Line 407... |
bcdh2 = bcdh - 6;
|
bcdh2 = bcdh - 6;
|
end
|
end
|
else begin
|
else begin
|
bcdh2 = bcdh;
|
bcdh2 = bcdh;
|
end
|
end
|
result = {bcdh2[3:0],bcdl[3:0]};
|
result[7:0] = {bcdh2[3:0],bcdl[3:0]};
|
end
|
end
|
end
|
end
|
|
|
// ASL - Arithmetic Shift Left
|
// ASL - Arithmetic Shift Left
|
ASL_ACC : begin
|
ASL_ACC : begin
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{STATUS[C],result} = {A,1'b0};
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{STATUS[C],result[7:0]} = {A,1'b0};
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STATUS[Z] = (result == 0) ? 1 : 0;
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STATUS[Z] = (result == 0) ? 1 : 0;
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STATUS[N] = result[7];
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STATUS[N] = result[7];
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end
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end
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ASL_ZPG, ASL_ZPX, ASL_ABS, ASL_ABX : begin
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ASL_ZPG, ASL_ZPX, ASL_ABS, ASL_ABX : begin
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{STATUS[C],result} = {alu_a,1'b0};
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{STATUS[C],result[7:0]} = {alu_a,1'b0};
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STATUS[Z] = (result == 0) ? 1 : 0;
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STATUS[Z] = (result == 0) ? 1 : 0;
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STATUS[N] = result[7];
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STATUS[N] = result[7];
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end
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end
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|
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// LSR - Logical Shift Right
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// LSR - Logical Shift Right
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LSR_ACC: begin
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LSR_ACC: begin
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{result,STATUS[C]} = {1'b0,A};
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{result[7:0],STATUS[C]} = {1'b0,A};
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STATUS[Z] = (result == 0) ? 1 : 0;
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STATUS[Z] = (result == 0) ? 1 : 0;
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STATUS[N] = result[7];
|
STATUS[N] = result[7];
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end
|
end
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LSR_ZPG, LSR_ZPX, LSR_ABS, LSR_ABX : begin
|
LSR_ZPG, LSR_ZPX, LSR_ABS, LSR_ABX : begin
|
{result,STATUS[C]} = {1'b0,alu_a};
|
{result[7:0],STATUS[C]} = {1'b0,alu_a};
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// ROL - Rotate Left
|
// ROL - Rotate Left
|
ROL_ACC : begin
|
ROL_ACC : begin
|
{STATUS[C],result} = {A,alu_status[C]};
|
{STATUS[C],result[7:0]} = {A,alu_status[C]};
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
ROL_ZPG, ROL_ZPX, ROL_ABS, ROL_ABX : begin
|
ROL_ZPG, ROL_ZPX, ROL_ABS, ROL_ABX : begin
|
{STATUS[C],result} = {alu_a,alu_status[C]};
|
{STATUS[C],result[7:0]} = {alu_a,alu_status[C]};
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// ROR - Rotate Right
|
// ROR - Rotate Right
|
ROR_ACC : begin
|
ROR_ACC : begin
|
{result,STATUS[C]} = {alu_status[C],A};
|
{result[7:0],STATUS[C]} = {alu_status[C],A};
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
ROR_ZPG, ROR_ZPX, ROR_ABS, ROR_ABX : begin
|
ROR_ZPG, ROR_ZPX, ROR_ABS, ROR_ABX : begin
|
{result, STATUS[C]} = {alu_status[C], alu_a};
|
{result[7:0], STATUS[C]} = {alu_status[C], alu_a};
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// CPX - Compare X Register
|
// CPX - Compare X Register
|
CPX_IMM, CPX_ZPG, CPX_ABS : begin
|
CPX_IMM, CPX_ZPG, CPX_ABS : begin
|
result = alu_x - alu_a;
|
result[7:0] = alu_x - alu_a;
|
STATUS[C] = (alu_x >= alu_a) ? 1 : 0;
|
STATUS[C] = (alu_x >= alu_a) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// CPY - Compare Y Register
|
// CPY - Compare Y Register
|
CPY_IMM, CPY_ZPG, CPY_ABS : begin
|
CPY_IMM, CPY_ZPG, CPY_ABS : begin
|
result = alu_y - alu_a;
|
result[7:0] = alu_y - alu_a;
|
STATUS[C] = (alu_y >= alu_a) ? 1 : 0;
|
STATUS[C] = (alu_y >= alu_a) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[Z] = (result == 0) ? 1 : 0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
