diff --git a/spicode.s65 b/spicode.s65
index ba1bb66..0a9da16 100644
--- a/spicode.s65
+++ b/spicode.s65
@@ -34,9 +34,11 @@ CODE_START:
 
 fmt_idx = $30
 out_idx = $31
+fmt_digit = $32
 .proc strf
     stz out_idx
     stz fmt_idx
+    stz fmt_digit
     ldx #0  ; index of format args
 @loop:
     ldy fmt_idx
@@ -57,9 +59,31 @@ out_idx = $31
         lda (ARG0),y  ; next char
         beq @null
         ; formats
+        cmp #'9'
+        ble @percent_number  ; numbers < letters
         cmp #'x'
         beq @format_hex1
         bra @normal_char
+@percent_number:
+            cmp #'1'
+            blt @normal_char  ; NaN or zero
+            ; todo covert from char
+            jsr hex_char_to_int  ; only 0-9 supported
+            ; A is now number of digits to convert
+            sta fmt_digit
+            iny
+            sty fmt_idx
+            lda (ARG0),y  ; next char
+            beq @null
+            cmp #'x'
+            beq @format_hexN 
+            bra @normal_char
+
+@format_hexN:
+                lda fmt_digit
+                jsr int_to_hex_str
+                bra @format_return
+
 @format_hex1:   ; 1 byte hex -> 2 chars
             lda ARG4,x
             phx
@@ -112,6 +136,17 @@ out_idx = $31
     rts
 .endproc
 
+; todo error handling
+.proc hex_char_to_int
+    cmp #'A'
+    bge @char
+    sbc #'0'
+    rts
+@char:
+    sbc #('A' - $A)
+    rts
+.endproc
+
 
 ;********************************************************************************
 ; @function Convert any int into hex