@@ -303,7 +303,21 @@ const OPCODES = {
303303 cpu . zeroFlag = cpu . Y ;
304304 }
305305 } ,
306- 0xA1 : "" ,
306+ 0xA1 : {
307+ name : "LDA (indirect,X)" , // Load Accumulator with Memory (Indirect Indexed Addressing with X)
308+ t : 6 , // Cycles required
309+ code : 0xA1 ,
310+ run : ( cpu ) => {
311+ const baseAddress = ( cpu . fetch ( ) + cpu . X ) & 0xFF ; // 0x00-0xFF (zeropage)
312+ const lowByte = cpu . memory . readByte ( baseAddress ) ;
313+ const highByte = cpu . memory . readByte ( ( baseAddress + 1 ) & 0xFF ) ; // wrap around in zeropage
314+ const address = ( highByte << 8 ) | lowByte ; // 16-bit address
315+
316+ cpu . ACC = cpu . memory . readByte ( address ) ;
317+ cpu . negativeFlag = cpu . ACC ;
318+ cpu . zeroFlag = cpu . ACC ;
319+ } ,
320+ } ,
307321 0xA2 : {
308322 name : "LDX #immediate" , // Load Index X with Memory
309323 t : 2 ,
@@ -316,7 +330,17 @@ const OPCODES = {
316330 } ,
317331 0xA3 : "" , // lax("(d,x)") // illegal
318332 0xA4 : "" ,
319- 0xA5 : "" ,
333+ 0xA5 : {
334+ name : "LDA zeropage" , // Load Accumulator with Memory from Zeropage
335+ t : 3 ,
336+ code : 0xA5 ,
337+ run : ( cpu ) => {
338+ const address = cpu . fetch ( ) ;
339+ cpu . ACC = cpu . memory . readByte ( address ) ;
340+ cpu . negativeFlag = cpu . ACC ;
341+ cpu . zeroFlag = cpu . ACC ;
342+ }
343+ } ,
320344 0xA6 : "" ,
321345 0xA7 : "" , // illegal
322346 0xA8 : {
@@ -351,23 +375,100 @@ const OPCODES = {
351375 } ,
352376 0xAB : "" , // lax("#i") // illegal
353377 0xAC : "" ,
354- 0xAD : "" ,
378+ 0xAD : {
379+ name : "LDA absolute" , // Load Accumulator Absolute
380+ t : 4 ,
381+ code : 0xAD ,
382+ run : ( cpu ) => {
383+ const lowByte = cpu . fetch ( ) ;
384+ const highByte = cpu . fetch ( ) ;
385+ const address = ( highByte << 8 ) | lowByte ;
386+ cpu . ACC = cpu . memory . readByte ( address ) ;
387+ cpu . negativeFlag = cpu . ACC ;
388+ cpu . zeroFlag = cpu . ACC ;
389+ }
390+ } ,
355391 0xAE : "" ,
356392 0xAF : "" , // lax("a") // illegal
357393 0xB0 : "" , // bcs("*+d")
358- 0xB1 : "" , // lda("(d),y")
394+ 0xB1 : {
395+ name : "LDA (indirect),Y" , // Load Accumulator with Memory (Indirect) and Indexed Addressing with Y
396+ t : 5 , // 5 (+1)
397+ code : 0xB1 ,
398+ run : ( cpu ) => {
399+ const baseAddress = cpu . fetch ( ) ;
400+ const lowByte = cpu . memory . readByte ( baseAddress ) ;
401+ const highByte = cpu . memory . readByte ( ( baseAddress + 1 ) & 0xFF ) ; // wrap around in zeropage
402+ const address = ( highByte << 8 ) | lowByte + cpu . Y ; // 16-bit address
403+
404+ // Check if the address crosses a page boundary
405+ if ( ( address & 0xFF00 ) !== ( ( highByte << 8 ) & 0xFF00 ) ) {
406+ cpu . cycles += 1 ; // Add an extra cycle if a page boundary is crossed
407+ }
408+
409+
410+ cpu . ACC = cpu . memory . readByte ( address ) ;
411+ cpu . negativeFlag = cpu . ACC ;
412+ cpu . zeroFlag = cpu . ACC ;
413+ } ,
414+ } ,
359415 0xB2 : "" , // stp_implied() // illegal
360416 0xB3 : "" , // lax("(d),y") // illegal
361417 0xB4 : "" ,
362- 0xB5 : "" ,
418+ 0xB5 : {
419+ name : "LDA zeropage,X" , // Load Accumulator with X-Indexed Zero Page
420+ t : 4 ,
421+ code : 0xB5 ,
422+ run : ( cpu ) => {
423+ const baseAddress = cpu . fetch ( ) ;
424+ const address = ( baseAddress + cpu . X ) & 0xFF ;
425+ cpu . ACC = cpu . memory . readByte ( address ) ;
426+ cpu . negativeFlag = cpu . ACC ;
427+ cpu . zeroFlag = cpu . ACC ;
428+ }
429+ } ,
363430 0xB6 : "" ,
364431 0xB7 : "" , // lax("d,y") // illegal
365432 0xB8 : "" , // clv_implied()
366- 0xB9 : "" , // lda("a,y")
433+ 0xB9 : {
434+ name : "LDA absolute,Y" , // Load Accumulator with Memory (Absolute Addressing with Y offset)
435+ t : 4 , // 4 (+1)
436+ code : 0xB9 ,
437+ run : ( cpu ) => {
438+ const lowByte = cpu . fetch ( ) ;
439+ const highByte = cpu . fetch ( ) ;
440+ const address = ( ( highByte << 8 ) | lowByte ) + cpu . Y ; // Combine bytes and add Y register value
441+ // Check if address crosses a page boundary
442+ if ( ( address & 0xFF00 ) !== ( ( highByte << 8 ) & 0xFF00 ) ) {
443+ cpu . cycles += 1 ; // Add an extra cycle if a page boundary is crossed
444+ }
445+
446+ cpu . ACC = cpu . memory . readByte ( address ) ;
447+ cpu . negativeFlag = cpu . ACC ;
448+ cpu . zeroFlag = cpu . ACC ;
449+ }
450+ } ,
367451 0xBA : "" , // tsx_implied()
368452 0xBB : "" , // las("a,y") // illegal
369453 0xBC : "" , // ldy("a,x")
370- 0xBD : "" , // lda("a,x")
454+ 0xBD : {
455+ name : "LDA absolute,X" , // Load Accumulator with Memory (Absolute Addressing with X offset)
456+ t : 4 , // 4 (+1)
457+ code : 0xBD ,
458+ run : ( cpu ) => {
459+ const lowByte = cpu . fetch ( ) ;
460+ const highByte = cpu . fetch ( ) ;
461+ const address = ( ( highByte << 8 ) | lowByte ) + cpu . X ; // Combine bytes and add X register value
462+ // Check if address crosses a page boundary
463+ if ( ( address & 0xFF00 ) !== ( ( highByte << 8 ) & 0xFF00 ) ) {
464+ cpu . cycles += 1 ; // Add an extra cycle if a page boundary is crossed
465+ }
466+
467+ cpu . ACC = cpu . memory . readByte ( address ) ;
468+ cpu . negativeFlag = cpu . ACC ;
469+ cpu . zeroFlag = cpu . ACC ;
470+ }
471+ } ,
371472 0xBE : "" , // ldx("a,y")
372473 0xBF : "" , // lax("a,y") // illegal
373474 0xC0 : "" , // cpy("#i")
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