diff --git a/compiler/src/prog8/compiler/target/c64/codegen/AsmGen.kt b/compiler/src/prog8/compiler/target/c64/codegen/AsmGen.kt
index a1af4e217..af5487811 100644
--- a/compiler/src/prog8/compiler/target/c64/codegen/AsmGen.kt
+++ b/compiler/src/prog8/compiler/target/c64/codegen/AsmGen.kt
@@ -1206,7 +1206,12 @@ $label              nop""")
     internal fun signExtendStackLsb(valueDt: DataType) {
         // sign extend signed byte on stack to signed word on stack
         when(valueDt) {
-            DataType.UBYTE -> out("  lda  #0 |  sta  P8ESTACK_HI+1,x")
+            DataType.UBYTE -> {
+                if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
+                    out("  stz  P8ESTACK_HI+1,x")
+                else
+                    out("  lda  #0 |  sta  P8ESTACK_HI+1,x")
+            }
             DataType.BYTE -> out("  jsr  prog8_lib.sign_extend_stack_byte")
             else -> throw AssemblyError("need byte type")
         }
@@ -1216,7 +1221,10 @@ $label              nop""")
         // sign extend signed byte in a var to a full word in that variable
         when(valueDt) {
             DataType.UBYTE -> {
-                out("  lda  #0 |  sta  $asmvar+1")
+                if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
+                    out("  stz  $asmvar+1")
+                else
+                    out("  lda  #0 |  sta  $asmvar+1")
             }
             DataType.BYTE -> {
                 out("""
diff --git a/compiler/src/prog8/compiler/target/c64/codegen/assignment/AssignmentAsmGen.kt b/compiler/src/prog8/compiler/target/c64/codegen/assignment/AssignmentAsmGen.kt
index 98b2004af..03e9bc4aa 100644
--- a/compiler/src/prog8/compiler/target/c64/codegen/assignment/AssignmentAsmGen.kt
+++ b/compiler/src/prog8/compiler/target/c64/codegen/assignment/AssignmentAsmGen.kt
@@ -1110,21 +1110,28 @@ internal class AssignmentAsmGen(private val program: Program, private val asmgen
         val sourceName = asmgen.asmVariableName(bytevar)
         when(wordtarget.kind) {
             TargetStorageKind.VARIABLE -> {
-                asmgen.out("""
-                    lda  $sourceName
-                    sta  ${wordtarget.asmVarname}
-                    lda  #0
-                    sta  ${wordtarget.asmVarname}+1
-                    """)
+                asmgen.out("  lda  $sourceName |  sta  ${wordtarget.asmVarname}")
+                if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
+                    asmgen.out("  stz  ${wordtarget.asmVarname}+1")
+                else
+                    asmgen.out("  lda  #0 |  sta  ${wordtarget.asmVarname}+1")
             }
             TargetStorageKind.ARRAY -> {
                 if (wordtarget.constArrayIndexValue!=null) {
                     val scaledIdx = wordtarget.constArrayIndexValue!! * 2
-                    asmgen.out(" lda  $sourceName  | sta  ${wordtarget.asmVarname}+$scaledIdx |  lda  #0  | sta  ${wordtarget.asmVarname}+$scaledIdx+1")
+                    asmgen.out("  lda  $sourceName  | sta  ${wordtarget.asmVarname}+$scaledIdx")
+                    if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
+                        asmgen.out("  stz  ${wordtarget.asmVarname}+$scaledIdx+1")
+                    else
+                        asmgen.out("  lda  #0  | sta  ${wordtarget.asmVarname}+$scaledIdx+1")
                 }
                 else {
                     asmgen.loadScaledArrayIndexIntoRegister(wordtarget.array!!, wordtarget.datatype, CpuRegister.Y)
-                    asmgen.out(" lda  $sourceName |  sta  ${wordtarget.asmVarname},y |  lda  #0 |  iny |  sta  ${wordtarget.asmVarname},y")
+                    asmgen.out("  lda  $sourceName |  sta  ${wordtarget.asmVarname},y |  iny")
+                    if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
+                        asmgen.out("  stz  ${wordtarget.asmVarname},y")
+                    else
+                        asmgen.out("  lda  #0 |  sta  ${wordtarget.asmVarname},y")
                 }
             }
             TargetStorageKind.REGISTER -> {
@@ -1136,12 +1143,11 @@ internal class AssignmentAsmGen(private val program: Program, private val asmgen
                 }
             }
             TargetStorageKind.STACK -> {
-                asmgen.out("""
-                    lda  $sourceName
-                    sta  P8ESTACK_LO,x
-                    lda  #0
-                    sta  P8ESTACK_HI,x
-                    dex""")
+                asmgen.out("  lda  $sourceName |  sta  P8ESTACK_LO,x")
+                if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
+                    asmgen.out("  stz  P8ESTACK_HI,x |  dex")
+                else
+                    asmgen.out("  lda  #0 |  sta  P8ESTACK_HI,x |  dex")
             }
             else -> throw AssemblyError("target type isn't word")
         }
@@ -1392,14 +1398,23 @@ internal class AssignmentAsmGen(private val program: Program, private val asmgen
                 TargetStorageKind.ARRAY -> {
                     if (target.array!!.indexer.indexNum!=null) {
                         val indexValue = target.array.indexer.constIndex()!! * DataType.FLOAT.memorySize()
-                        asmgen.out("""
-                            lda  #0
-                            sta  ${target.asmVarname}+$indexValue
-                            sta  ${target.asmVarname}+$indexValue+1
-                            sta  ${target.asmVarname}+$indexValue+2
-                            sta  ${target.asmVarname}+$indexValue+3
-                            sta  ${target.asmVarname}+$indexValue+4
-                        """)
+                        if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
+                            asmgen.out("""
+                                stz  ${target.asmVarname}+$indexValue
+                                stz  ${target.asmVarname}+$indexValue+1
+                                stz  ${target.asmVarname}+$indexValue+2
+                                stz  ${target.asmVarname}+$indexValue+3
+                                stz  ${target.asmVarname}+$indexValue+4
+                            """)
+                        else
+                            asmgen.out("""
+                                lda  #0
+                                sta  ${target.asmVarname}+$indexValue
+                                sta  ${target.asmVarname}+$indexValue+1
+                                sta  ${target.asmVarname}+$indexValue+2
+                                sta  ${target.asmVarname}+$indexValue+3
+                                sta  ${target.asmVarname}+$indexValue+4
+                            """)
                     } else {
                         val asmvarname = asmgen.asmVariableName(target.array.indexer.indexVar!!)
                         asmgen.out("""
@@ -1561,12 +1576,11 @@ internal class AssignmentAsmGen(private val program: Program, private val asmgen
         if (address != null) {
             when(wordtarget.kind) {
                 TargetStorageKind.VARIABLE -> {
-                    asmgen.out("""
-                        lda  ${address.toHex()}
-                        sta  ${wordtarget.asmVarname}
-                        lda  #0
-                        sta  ${wordtarget.asmVarname}+1
-                        """)
+                    asmgen.out("  lda  ${address.toHex()} |  sta  ${wordtarget.asmVarname}")
+                    if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
+                        asmgen.out("  stz  ${wordtarget.asmVarname}+1")
+                    else
+                        asmgen.out("  lda  #0 |  sta  ${wordtarget.asmVarname}+1")
                 }
                 TargetStorageKind.ARRAY -> {
                     throw AssemblyError("no asm gen for assign memory byte at $address to array ${wordtarget.asmVarname}")
@@ -1578,12 +1592,11 @@ internal class AssignmentAsmGen(private val program: Program, private val asmgen
                     else -> throw AssemblyError("word regs can only be pair")
                 }
                 TargetStorageKind.STACK -> {
-                    asmgen.out("""
-                        lda  ${address.toHex()}
-                        sta  P8ESTACK_LO,x
-                        lda  #0
-                        sta  P8ESTACK_HI,x
-                        dex""")
+                    asmgen.out("  lda  ${address.toHex()} |  sta  P8ESTACK_LO,x")
+                    if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
+                        asmgen.out("  stz  P8ESTACK_HI,x |  dex")
+                    else
+                        asmgen.out("  lda  #0 |  sta  P8ESTACK_HI,x |  dex")
                 }
                 else -> throw AssemblyError("other types aren't word")
             }
@@ -1591,7 +1604,11 @@ internal class AssignmentAsmGen(private val program: Program, private val asmgen
             when(wordtarget.kind) {
                 TargetStorageKind.VARIABLE -> {
                     asmgen.loadByteFromPointerIntoA(identifier)
-                    asmgen.out(" sta  ${wordtarget.asmVarname} |  lda  #0 |  sta ${wordtarget.asmVarname}+1")
+                    asmgen.out(" sta  ${wordtarget.asmVarname}")
+                    if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
+                        asmgen.out("  stz  ${wordtarget.asmVarname}+1")
+                    else
+                        asmgen.out("  lda  #0 |  sta  ${wordtarget.asmVarname}+1")
                 }
                 TargetStorageKind.ARRAY -> {
                     throw AssemblyError("no asm gen for assign memory byte $identifier to array ${wordtarget.asmVarname} ")
@@ -1607,7 +1624,11 @@ internal class AssignmentAsmGen(private val program: Program, private val asmgen
                 }
                 TargetStorageKind.STACK -> {
                     asmgen.loadByteFromPointerIntoA(identifier)
-                    asmgen.out(" sta  P8ESTACK_LO,x |  lda  #0 |  sta  P8ESTACK_HI,x |  dex")
+                    asmgen.out("  sta  P8ESTACK_LO,x")
+                    if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
+                        asmgen.out("  stz  P8ESTACK_HI,x |  dex")
+                    else
+                        asmgen.out("  lda  #0 |  sta  P8ESTACK_HI,x |  dex")
                 }
                 else -> throw AssemblyError("other types aren't word")
             }
diff --git a/compiler/src/prog8/compiler/target/c64/codegen/assignment/AugmentableAssignmentAsmGen.kt b/compiler/src/prog8/compiler/target/c64/codegen/assignment/AugmentableAssignmentAsmGen.kt
index e1969d748..3a348bcdc 100644
--- a/compiler/src/prog8/compiler/target/c64/codegen/assignment/AugmentableAssignmentAsmGen.kt
+++ b/compiler/src/prog8/compiler/target/c64/codegen/assignment/AugmentableAssignmentAsmGen.kt
@@ -643,14 +643,24 @@ internal class AugmentableAssignmentAsmGen(private val program: Program,
                     sta  $name""")
             }
             "<<" -> {
-                if(value>=8) asmgen.out(" lda  #0 |  sta  $name")
-                else repeat(value) { asmgen.out(" asl  $name") }
+                if(value>=8) {
+                    if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
+                        asmgen.out("  stz  $name")
+                    else
+                        asmgen.out("  lda  #0 |  sta  $name")
+                }
+                else repeat(value) { asmgen.out("  asl  $name") }
             }
             ">>" -> {
                 if(value>0) {
                     if (dt == DataType.UBYTE) {
-                        if(value>=8) asmgen.out(" lda  #0 |  sta  $name")
-                        else repeat(value) { asmgen.out(" lsr  $name") }
+                        if(value>=8) {
+                            if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
+                                asmgen.out("  stz  $name")
+                            else
+                                asmgen.out("  lda  #0 |  sta  $name")
+                        }
+                        else repeat(value) { asmgen.out("  lsr  $name") }
                     } else {
                         when {
                             value>=8 -> asmgen.out("""
@@ -665,7 +675,7 @@ internal class AugmentableAssignmentAsmGen(private val program: Program,
                                 ldy  #$value
                                 jsr  math.lsr_byte_A
                                 sta  $name""")
-                            else -> repeat(value) { asmgen.out(" lda  $name | asl  a |  ror  $name") }
+                            else -> repeat(value) { asmgen.out("  lda  $name | asl  a |  ror  $name") }
                         }
                     }
                 }
@@ -858,8 +868,19 @@ internal class AugmentableAssignmentAsmGen(private val program: Program,
             }
             "<<" -> {
                 when {
-                    value>=16 -> asmgen.out(" lda  #0 |  sta  $name |  sta  $name+1")
-                    value==8 -> asmgen.out(" lda  $name |  sta  $name+1 |  lda  #0 |  sta  $name")
+                    value>=16 -> {
+                        if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
+                            asmgen.out("  stz  $name |  stz  $name+1")
+                        else
+                            asmgen.out("  lda  #0 |  sta  $name |  sta  $name+1")
+                    }
+                    value==8 -> {
+                        asmgen.out("  lda  $name |  sta  $name+1")
+                        if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
+                            asmgen.out("  stz  $name")
+                        else
+                            asmgen.out("  lda  #0 |  sta  $name")
+                    }
                     value>2 -> asmgen.out("""
                         ldy  #$value
 -                       asl  $name
@@ -874,8 +895,19 @@ internal class AugmentableAssignmentAsmGen(private val program: Program,
                 if (value > 0) {
                     if(dt==DataType.UWORD) {
                         when {
-                            value>=16 -> asmgen.out(" lda  #0 |  sta  $name |  sta  $name+1")
-                            value==8 -> asmgen.out(" lda  $name+1 |  sta  $name |  lda  #0 |  sta  $name+1")
+                            value>=16 -> {
+                                if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
+                                    asmgen.out("  stz  $name |  stz  $name+1")
+                                else
+                                    asmgen.out("  lda  #0 |  sta  $name |  sta  $name+1")
+                            }
+                            value==8 -> {
+                                asmgen.out("  lda  $name+1 |  sta  $name")
+                                if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
+                                    asmgen.out("  stz  $name+1")
+                                else
+                                    asmgen.out("  lda  #0 |  sta  $name+1")
+                            }
                             value>2 -> asmgen.out("""
                                 ldy  #$value
 -                               lsr  $name+1
@@ -921,41 +953,41 @@ internal class AugmentableAssignmentAsmGen(private val program: Program,
                 when {
                     value == 0 -> {
                         if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
-                            asmgen.out(" stz  $name |  stz  $name+1")
+                            asmgen.out("  stz  $name |  stz  $name+1")
                         else
-                            asmgen.out(" lda  #0 |  sta  $name |  sta  $name+1")
+                            asmgen.out("  lda  #0 |  sta  $name |  sta  $name+1")
                     }
                     value and 255 == 0 -> {
                         if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
-                            asmgen.out(" stz  $name")
+                            asmgen.out("  stz  $name")
                         else
-                            asmgen.out(" lda  #0 |  sta  $name")
-                        asmgen.out(" lda  $name+1 |  and  #>$value |  sta  $name+1")
+                            asmgen.out("  lda  #0 |  sta  $name")
+                        asmgen.out("  lda  $name+1 |  and  #>$value |  sta  $name+1")
                     }
                     value < 0x0100 -> {
-                        asmgen.out(" lda  $name |  and  #$value |  sta  $name")
+                        asmgen.out("  lda  $name |  and  #$value |  sta  $name")
                         if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
                             asmgen.out("  stz  $name+1")
                         else
                             asmgen.out("  lda  #0 |  sta  $name+1")
                     }
-                    else -> asmgen.out(" lda  $name |  and  #<$value |  sta  $name |  lda  $name+1 |  and  #>$value |  sta  $name+1")
+                    else -> asmgen.out("  lda  $name |  and  #<$value |  sta  $name |  lda  $name+1 |  and  #>$value |  sta  $name+1")
                 }
             }
             "^" -> {
                 when {
                     value == 0 -> {}
-                    value and 255 == 0 -> asmgen.out(" lda  $name+1 |  eor  #>$value |  sta  $name+1")
-                    value < 0x0100 -> asmgen.out(" lda  $name |  eor  #$value |  sta  $name")
-                    else -> asmgen.out(" lda  $name |  eor  #<$value |  sta  $name |  lda  $name+1 |  eor  #>$value |  sta  $name+1")
+                    value and 255 == 0 -> asmgen.out("  lda  $name+1 |  eor  #>$value |  sta  $name+1")
+                    value < 0x0100 -> asmgen.out("  lda  $name |  eor  #$value |  sta  $name")
+                    else -> asmgen.out("  lda  $name |  eor  #<$value |  sta  $name |  lda  $name+1 |  eor  #>$value |  sta  $name+1")
                 }
             }
             "|" -> {
                 when {
                     value == 0 -> {}
-                    value and 255 == 0 -> asmgen.out(" lda  $name+1 |  ora  #>$value |  sta  $name+1")
-                    value < 0x0100 -> asmgen.out(" lda  $name |  ora  #$value |  sta  $name")
-                    else -> asmgen.out(" lda  $name |  ora  #<$value |  sta  $name |  lda  $name+1 |  ora  #>$value |  sta  $name+1")
+                    value and 255 == 0 -> asmgen.out("  lda  $name+1 |  ora  #>$value |  sta  $name+1")
+                    value < 0x0100 -> asmgen.out("  lda  $name |  ora  #$value |  sta  $name")
+                    else -> asmgen.out("  lda  $name |  ora  #<$value |  sta  $name |  lda  $name+1 |  ora  #>$value |  sta  $name+1")
                 }
             }
             else -> throw AssemblyError("invalid operator for in-place modification $operator")
@@ -1019,11 +1051,12 @@ internal class AugmentableAssignmentAsmGen(private val program: Program,
                                 sta  $name+1""")
                     }
                     "*" -> {
+                        asmgen.out("  lda  $otherName |  sta  P8ZP_SCRATCH_W1")
+                        if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
+                            asmgen.out("  stz  P8ZP_SCRATCH_W1+1")
+                        else
+                            asmgen.out("  lda  #0 |  sta  P8ZP_SCRATCH_W1+1")
                         asmgen.out("""
-                            lda  $otherName
-                            sta  P8ZP_SCRATCH_W1
-                            lda  #0
-                            sta  P8ZP_SCRATCH_W1+1
                             lda  $name
                             ldy  $name+1
                             jsr  math.multiply_words
@@ -1068,12 +1101,16 @@ internal class AugmentableAssignmentAsmGen(private val program: Program,
                         }
                     }
                     "&" -> {
-                        asmgen.out(" lda  $otherName |  and  $name |  sta  $name")
-                        if(dt in WordDatatypes)
-                            asmgen.out(" lda  #0 |  sta  $name+1")
+                        asmgen.out("  lda  $otherName |  and  $name |  sta  $name")
+                        if(dt in WordDatatypes) {
+                            if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
+                                asmgen.out("  stz  $name+1")
+                            else
+                                asmgen.out("  lda  #0 |  sta  $name+1")
+                        }
                     }
-                    "^" -> asmgen.out(" lda  $otherName |  eor  $name |  sta  $name")
-                    "|" -> asmgen.out(" lda  $otherName |  ora  $name |  sta  $name")
+                    "^" -> asmgen.out("  lda  $otherName |  eor  $name |  sta  $name")
+                    "|" -> asmgen.out("  lda  $otherName |  ora  $name |  sta  $name")
                     else -> throw AssemblyError("invalid operator for in-place modification $operator")
                 }
             }
@@ -1081,8 +1118,8 @@ internal class AugmentableAssignmentAsmGen(private val program: Program,
                 // the value is a proper 16-bit word, so use both bytes of it.
                 when (operator) {
                     // note: ** (power) operator requires floats.
-                    "+" -> asmgen.out(" lda  $name |  clc |  adc  $otherName |  sta  $name |  lda  $name+1 |  adc  $otherName+1 |  sta  $name+1")
-                    "-" -> asmgen.out(" lda  $name |  sec |  sbc  $otherName |  sta  $name |  lda  $name+1 |  sbc  $otherName+1 |  sta  $name+1")
+                    "+" -> asmgen.out("  lda  $name |  clc |  adc  $otherName |  sta  $name |  lda  $name+1 |  adc  $otherName+1 |  sta  $name+1")
+                    "-" -> asmgen.out("  lda  $name |  sec |  sbc  $otherName |  sta  $name |  lda  $name+1 |  sbc  $otherName+1 |  sta  $name+1")
                     "*" -> {
                         asmgen.out("""
                             lda  $otherName
@@ -1322,8 +1359,12 @@ internal class AugmentableAssignmentAsmGen(private val program: Program,
                     "&" -> {
                         asmgen.assignExpressionToRegister(value, RegisterOrPair.A)
                         asmgen.out("  and  $name |  sta  $name")
-                        if(dt in WordDatatypes)
-                            asmgen.out(" lda  #0 |  sta  $name+1")
+                        if(dt in WordDatatypes) {
+                            if(CompilationTarget.instance.machine.cpu == CpuType.CPU65c02)
+                                asmgen.out("  stz  $name+1")
+                            else
+                                asmgen.out("  lda  #0 |  sta  $name+1")
+                        }
                     }
                     "^" -> {
                         asmgen.assignExpressionToRegister(value, RegisterOrPair.A)
diff --git a/docs/source/todo.rst b/docs/source/todo.rst
index fa1108b6b..2bc492e6f 100644
--- a/docs/source/todo.rst
+++ b/docs/source/todo.rst
@@ -2,7 +2,6 @@
 TODO
 ====
 
-- use 'stz' more on cx16 when setting variables to zero or clearing a word's msb etc.
 - see if we can group some errors together for instance the (now single) errors about unidentified symbols
 - Cx16 target: support full-screen 640x480 and 320x240 graphics? That requires our own custom graphics routines though to draw lines.
 - make it possible to use cpu opcodes such as 'nop' as variable names by prefixing all asm vars with something such as '_'
diff --git a/examples/test.p8 b/examples/test.p8
index 11a9cb9b2..ddd2aa14e 100644
--- a/examples/test.p8
+++ b/examples/test.p8
@@ -9,7 +9,7 @@ main {
         ubyte ub1
         ubyte ub2
 
-        uw = ub1 as uword + ub2     ; fairly ok asm  (TODO make it use stz on cx16)
+        uw = ub1 as uword + ub2     ; fairly ok asm.. but the next though...:
         ub1++
         uw = ub1 + ub2          ; TODO horrible asm using the eval stack... fix