I understood that the Heidenhain TNC 151 controllers obeyed Heidenhain's own codes and not normal G code, BUT I've seen an oblique reference in an online operators guide to being able to enter normal G codes, and there being a clip on overlay held on by magnets to customise the controls keyboard (presumably just the legends).
Anyone any experience of this - is it only certain firmware levels that do it - spill the beans !!
The manual in question is at:
Open the TNC 151B User manual and search for Programing in ISO codes