diff --git a/codeGenCpu6502/src/prog8/codegen/cpu6502/assignment/AugmentableAssignmentAsmGen.kt b/codeGenCpu6502/src/prog8/codegen/cpu6502/assignment/AugmentableAssignmentAsmGen.kt
index 399790a11..0867188f0 100644
--- a/codeGenCpu6502/src/prog8/codegen/cpu6502/assignment/AugmentableAssignmentAsmGen.kt
+++ b/codeGenCpu6502/src/prog8/codegen/cpu6502/assignment/AugmentableAssignmentAsmGen.kt
@@ -208,10 +208,23 @@ internal class AugmentableAssignmentAsmGen(private val program: PtProgram,
             TargetStorageKind.ARRAY -> {
                 val indexNum = target.array!!.index as? PtNumber
                 if (indexNum!=null) {
-                    val targetVarName = if(target.array.splitWords)
-                        "${target.asmVarname} + ${indexNum.number.toInt()}"
-                    else
-                        "${target.asmVarname} + ${indexNum.number.toInt()*program.memsizer.memorySize(target.datatype)}"
+                    val index = indexNum.number.toInt()
+                    if(target.array.splitWords) {
+                        when(value.kind) {
+                            SourceStorageKind.LITERALNUMBER -> inplacemodificationSplitWordWithLiteralval(target.asmVarname, index, operator, value.number!!.number.toInt())
+                            else -> {
+                                // TODO: more optimized code for VARIABLE, REGISTER, MEMORY, ARRAY, EXPRESSION in the case of split-word arrays
+                                val scope = target.origAstTarget?.definingSub()
+                                val regTarget = AsmAssignTarget.fromRegisters(RegisterOrPair.R0, false, target.position, scope, asmgen)
+                                val assignToReg = AsmAssignment(value, regTarget, program.memsizer, target.position)
+                                assignmentAsmGen.translateNormalAssignment(assignToReg, scope)
+                                inplacemodificationSplitWordWithR0(target.asmVarname, index, operator)
+                            }
+                        }
+                        return
+                    }
+                    // normal array
+                    val targetVarName = "${target.asmVarname} + ${index*program.memsizer.memorySize(target.datatype)}"
                     when (target.datatype) {
                         in ByteDatatypes -> {
                             when(value.kind) {
@@ -458,6 +471,91 @@ internal class AugmentableAssignmentAsmGen(private val program: PtProgram,
         }
     }
 
+    private fun inplacemodificationSplitWordWithR0(arrayVar: String, index: Int, operator: String) {
+        when (operator) {
+            "+" -> {
+                asmgen.out("""
+                    lda  ${arrayVar}_lsb+$index
+                    clc
+                    adc  cx16.r0L
+                    sta  ${arrayVar}_lsb+$index
+                    lda  ${arrayVar}_msb+$index
+                    adc  cx16.r0H
+                    sta  ${arrayVar}_msb+$index""")
+            }
+            "-" -> {
+                asmgen.out("""
+                    lda  ${arrayVar}_lsb+$index
+                    sec
+                    sbc  cx16.r0L
+                    sta  ${arrayVar}_lsb+$index
+                    lda  ${arrayVar}_msb+$index
+                    sbc  cx16.r0H
+                    sta  ${arrayVar}_msb+$index""")
+            }
+            else -> TODO("in-place modify split-words array value for operator $operator")
+        }
+    }
+
+    private fun inplacemodificationSplitWordWithLiteralval(arrayVar: String, index: Int, operator: String, value: Int) {
+        // note: this contains special optimized cases because we know the exact value. Don't replace this with another routine.
+        when (operator) {
+            "+" -> {
+                when {
+                    value==0 -> {}
+                    value in 1..0xff -> asmgen.out("""
+                        lda  ${arrayVar}_lsb+$index
+                        clc
+                        adc  #$value
+                        sta  ${arrayVar}_lsb+$index
+                        bcc  +
+                        inc  ${arrayVar}_msb+$index
++""")
+                    value==0x0100 -> asmgen.out(" inc  ${arrayVar}_msb+$index")
+                    value==0x0200 -> asmgen.out(" inc  ${arrayVar}_msb+$index |  inc  ${arrayVar}_msb+$index")
+                    value==0x0300 -> asmgen.out(" inc  ${arrayVar}_msb+$index |  inc  ${arrayVar}_msb+$index |  inc  ${arrayVar}_msb+$index")
+                    value==0x0400 -> asmgen.out(" inc  ${arrayVar}_msb+$index |  inc  ${arrayVar}_msb+$index |  inc  ${arrayVar}_msb+$index |  inc  ${arrayVar}_msb+$index")
+                    value and 255==0 -> asmgen.out(" lda  ${arrayVar}_msb+$index |  clc |  adc  #>$value |  sta  ${arrayVar}_msb+$index")
+                    else -> asmgen.out("""
+                        lda  ${arrayVar}_lsb+$index
+                        clc
+                        adc  #<$value
+                        sta  ${arrayVar}_lsb+$index
+                        lda  ${arrayVar}_msb+$index
+                        adc  #>$value
+                        sta  ${arrayVar}_msb+$index""")
+                }
+            }
+            "-" -> {
+                when {
+                    value==0 -> {}
+                    value in 1..0xff -> asmgen.out("""
+                        lda  ${arrayVar}_lsb+$index
+                        sec
+                        sbc  #$value
+                        sta  ${arrayVar}_lsb+$index
+                        bcs  +
+                        dec  ${arrayVar}_msb+$index
++""")
+                    value==0x0100 -> asmgen.out(" dec  ${arrayVar}_msb+$index")
+                    value==0x0200 -> asmgen.out(" dec  ${arrayVar}_msb+$index |  dec  ${arrayVar}_msb+$index")
+                    value==0x0300 -> asmgen.out(" dec  ${arrayVar}_msb+$index |  dec  ${arrayVar}_msb+$index |  dec  ${arrayVar}_msb+$index")
+                    value==0x0400 -> asmgen.out(" dec  ${arrayVar}_msb+$index |  dec  ${arrayVar}_msb+$index |  dec  ${arrayVar}_msb+$index |  dec  ${arrayVar}_msb+$index")
+                    value and 255==0 -> asmgen.out(" lda  ${arrayVar}_msb+$index |  sec |  sbc  #>$value |  sta  ${arrayVar}_msb+$index")
+                    else -> asmgen.out("""
+                        lda  ${arrayVar}_lsb+$index
+                        sec
+                        sbc  #<$value
+                        sta  ${arrayVar}_lsb+$index
+                        lda  ${arrayVar}_msb+$index
+                        sbc  #>$value
+                        sta  ${arrayVar}_msb+$index""")
+                }
+            }
+            else -> TODO("in-place modify split-words array value for operator $operator") 
+        }
+    }
+
     private fun inplacemodificationRegisterAXwithVariable(operator: String, variable: String, varDt: DataType): Boolean {
         when(operator) {
             "+" -> {
diff --git a/examples/test.p8 b/examples/test.p8
index e70b2accd..5a3b1139f 100644
--- a/examples/test.p8
+++ b/examples/test.p8
@@ -5,16 +5,53 @@
 
 main {
     sub start() {
-        ubyte @shared xx
-        uword[3] ubarr
-        bool[3] barr
-        float[3] flarr
-        bool @shared bb
+        ubyte @shared index = 1
 
-        ubarr[1] = ubarr[1] < 2
-        ubarr[1] = ubarr[1] <= 2
-        ubarr[1] = ubarr[1] > 3
-        ubarr[1] = ubarr[1] >= 3
+;        @(2000) = 99
+;        uword @shared ptr = 2000
+;        txt.print_ub(@(2000))
+;        txt.nl()
+;        @(2000) ++
+;        @(2000) ++
+;        @(2000) --
+;        txt.print_ub(@(2000))
+;        txt.nl()
+
+
+        uword[3] @split arr
+
+        arr[1] = 9999
+        txt.print_uw(arr[1])
+        txt.nl()
+        arr[1] = arr[1]*5
+        cx16.r0=2222
+        arr[1] *= cx16.r0
+        arr[1] -=5
+        arr[1] -=index
+        txt.print_uw(arr[1])
+        txt.nl()
+
+;        arr[index] = 9999
+;        txt.print_uw(arr[index])
+;        txt.nl()
+;        arr[index] += 5
+;        arr[index] += 5
+;        arr[index] -= 5
+;        txt.print_uw(arr[index])
+;        txt.nl()
+
+
+;
+;        ubyte @shared xx
+;        uword[3] ubarr
+;        bool[3] barr
+;        float[3] flarr
+;        bool @shared bb
+;
+;        ubarr[1] = ubarr[1] < 2
+;        ubarr[1] = ubarr[1] <= 2
+;        ubarr[1] = ubarr[1] > 3
+;        ubarr[1] = ubarr[1] >= 3
 
 ;        barr[1] = barr[0] and barr[2]
 ;        barr[1] = barr[0] or barr[2]