Add warning about ttf extended ASCII.

FONT_TO_PY.md

@@ -44,6 +44,10 @@ Example usage to produce a file ``myfont.py`` with height of 23 pixels:
 Any requirement for arguments -xr will be specified in the device driver
 documentation. Bit reversal is required by some display hardware.
 
+Note that producing extended ASCII characters (ordinal value > 127) from ttf
+files seems unreliable. If the expected results are not achieved, use an otf
+font. This appears to be a limitation of the `freetype` library.
+
 ### Output
 
 The specified height is a target. The algorithm gets as close to the target

font_to_py.py

@@ -517,6 +517,8 @@ if __name__ == "__main__":
 
         if args.largest > 255:
             quit('--largest must be < 256')
+        elif args.largest > 127 and os.path.splitext(args.infile)[1].upper() == '.TTF':
+            print('WARNING: extended ASCII characters may not be correctly converted. See docs.')
 
         if args.errchar < 0 or args.errchar > 255:
             quit('--errchar must be between 0 and 255')