diff --git a/firmware/screencode.h b/firmware/screencode.h
new file mode 100644
index 0000000..c50ac4a
--- /dev/null
+++ b/firmware/screencode.h
@@ -0,0 +1,53 @@
+; Convert characters to screen codes
+; Modified to pass through codes below 12
+
+; Helper macro that converts and outputs one character
+.macro _screencode char
+        .if (char < 256)
+            .if (char > 11)
+                .byte (char | $80)
+            .else
+                .byte (char)
+            .endif
+        .else
+                .error  "screencode: Character constant out of range"
+        .endif
+.endmacro
+
+.macro  screencode arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9
+
+        ; Bail out if next argument is empty
+        .if     .blank (arg1)
+                .exitmacro
+        .endif
+
+        ; Check for a string
+        .if     .match ({arg1}, "")
+
+                ; Walk over all string chars
+                .repeat .strlen (arg1), i
+                        _screencode        {.strat (arg1, i)}
+                .endrepeat
+
+        ; Check for a number
+        .elseif .match (.left (1, {arg1}), 0)
+
+                ; Just output the number
+                _screencode        arg1
+
+        ; Check for a character
+        .elseif .match (.left (1, {arg1}), 'a')
+
+                ; Just output the character
+                _screencode        arg1
+
+        ; Anything else is an error
+        .else
+
+                .error  "screencode: invalid argument type"
+
+        .endif
+
+        ; Call the macro recursively with the remaining args
+        screencode arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9
+.endmacro