diff --git a/codeGenCpu6502/src/prog8/codegen/cpu6502/assignment/AssignmentAsmGen.kt b/codeGenCpu6502/src/prog8/codegen/cpu6502/assignment/AssignmentAsmGen.kt
index 15d49bd4a..adbdd93b0 100644
--- a/codeGenCpu6502/src/prog8/codegen/cpu6502/assignment/AssignmentAsmGen.kt
+++ b/codeGenCpu6502/src/prog8/codegen/cpu6502/assignment/AssignmentAsmGen.kt
@@ -420,11 +420,12 @@ internal class AssignmentAsmGen(private val program: PtProgram,
             return name
         }
 
-
+        asmgen.out("    ; rpn expression @ ${value.position}  ${value.children.size} nodes")  // TODO
         var depth=0
         value.children.forEach {
             when (it) {
                 is PtRpnOperator -> {
+                    asmgen.out("    ; rpn child node ${it.operator}")  // TODO
                     val rightvar = evalVars.getValue(getVarDt(it.rightType)).pop()
                     val leftvar = evalVars.getValue(getVarDt(it.leftType)).pop()
                     depth-=2
@@ -454,6 +455,7 @@ internal class AssignmentAsmGen(private val program: PtProgram,
                     }
                 }
                 is PtExpression -> {
+                    asmgen.out("    ; rpn child node expr ${it}")  // TODO
                     val varname = evalVarName(it.type, depth)
                     assignExpressionToVariable(it, varname, it.type)
                     depth++
@@ -461,14 +463,30 @@ internal class AssignmentAsmGen(private val program: PtProgram,
                 else -> throw AssemblyError("weird rpn node")
             }
         }
+        asmgen.out("    ; DONE rpn expression @ ${value.position}")  // TODO
+
         require(depth==1) { "unbalanced RPN: $depth  ${value.position}" }
+        asmgen.out("    ; assign rpn result to target")   // TODO
         val resultVariable = evalVars.getValue(getVarDt(value.type)).pop()
-        when(assign.target.datatype) {
-            in ByteDatatypes -> assignVariableByte(assign.target, resultVariable)
-            in WordDatatypes -> assignVariableWord(assign.target, resultVariable)
-            DataType.FLOAT -> assignVariableFloat(assign.target, resultVariable)
-            else -> throw AssemblyError("weird dt")
+        if(assign.target.datatype != value.type) {
+            // we only allow for transparent byte -> word / ubyte -> uword assignments
+            // any other type difference is an error
+            if(assign.target.datatype in WordDatatypes && value.type in ByteDatatypes) {
+                assignVariableToRegister(resultVariable, RegisterOrPair.A, value.type==DataType.BYTE, scope, assign.position)
+                asmgen.signExtendAYlsb(value.type)
+                assignRegisterpairWord(assign.target, RegisterOrPair.AY)
+            } else {
+                throw AssemblyError("data type mismatch, missing typecast ${value.type} -> ${assign.target.datatype}")
+            }
+        } else {
+            when (value.type) {
+                in ByteDatatypes -> assignVariableByte(assign.target, resultVariable)
+                in WordDatatypes -> assignVariableWord(assign.target, resultVariable)
+                DataType.FLOAT -> assignVariableFloat(assign.target, resultVariable)
+                else -> throw AssemblyError("weird dt")
+            }
         }
+        asmgen.out("    ; DONE assign rpn result to target")   // TODO
 
         require(evalVars.all { it.value.isEmpty() }) { "invalid rpn evaluation" }
 
diff --git a/docs/source/todo.rst b/docs/source/todo.rst
index dfcd71c79..e457f6b18 100644
--- a/docs/source/todo.rst
+++ b/docs/source/todo.rst
@@ -1,18 +1,22 @@
 TODO
 ====
-RPN: examples/turtlegfx crashes
 RPN: examples/maze crashes
+RPN: Fix the TODO RPN routines to be optimized assembly in RpnExpressionAsmGen.kt
+RPN: check BinExprSplitter disablement any effect for RPN?
+then:
 RPN: examples/bsieve,charset compilation crash (bit shift expression)
 RPN: cube3d-float is massive and slow
 RPN: mandelbrot is big, but seems faster
 RPN: swirl is MUCH slower, wizzine is slower
-
-RPN: Fix the TODO RPN routines to be optimized assembly in RpnExpressionAsmGen.kt
+then:
 RPN: check BinExprSplitter disablement any effect for RPN?
 RPN: Implement RPN codegen for IR.
 
+
 For next minor release
 ^^^^^^^^^^^^^^^^^^^^^^
+- ubyte fits = cx<numCellsHoriz-1   much larger code than when declared as bool.  (RPN only?)
+- if fits and @(celladdr(cx+1))  much larger code than   if fits and not @(celladdr(cx+1))   (RPN only?)
 - Move asmExtra vars into BSS as well, now are .byte 0 allocated
 
 ...
diff --git a/examples/test.p8 b/examples/test.p8
index 23e7dc5ec..94a34a87c 100644
--- a/examples/test.p8
+++ b/examples/test.p8
@@ -1,21 +1,37 @@
-%import math
 %import textio
 %zeropage basicsafe
 
-; Note: this program is compatible with C64 and CX16.
-
 main {
+    const ubyte numCellsHoriz = 15 ;(screenwidth-1) / 2
+    const ubyte numCellsVert = 7 ; (screenheight-1) / 2
 
-    sub start() {
-        bool x
-        ubyte y
-        repeat 20 {
-            x = math.rnd() & 1
-            y = ((math.rnd()&1)!=0)
-            txt.print_ub(x)
-            txt.spc()
-            txt.print_ub(y)
-            txt.nl()
+    ; cell properties
+    const ubyte RIGHT = 2
+    ubyte[256] cells = 0
+
+    sub generate() {
+        ubyte cx = 0
+        cells[0] = 255
+        repeat 40 {
+            bool fits = cx<numCellsHoriz
+            if fits and not @(celladdr(cx+1)) {         ; TODO evaluated wrong in RPN! Only as part of IF, and using celladdr()
+                cx++
+                cells[cx] = 255
+            }
         }
+        txt.print_ub(cx)
+        txt.print(" should be ")
+        txt.print_ub(numCellsHoriz)
+    }
+
+    sub celladdr(ubyte cx) -> uword {
+        return &cells+cx
+    }
+
+    sub start()  {
+        generate()
+        txt.nl()
+        txt.nl()
     }
 }
+