The simplest, but one of the most practically useful mappings of the bitplanes, is to permute them; in slightly greater generality some particular plane, its complement, or a constant value might be assigned to each plane. The CAMEX function apzoc("pqrs") serves this purpose. Each of its four arguments can take one of the values
assuming the bitplanes to follow the same order as the arguments. Thus apzoc("badc") would imply the exchange of the even planes with the odd planes, apzoc("cdab") the exchange of CAM-A with CAM-B , apzoc("Dabc") a long cycle in which plane 3 is complemented as it is copied into plane 0.
The simpler mnemonics afforded by these letters is why apzoc has a character string argument rather than using plane numbers directly. Otherwise it is hard to find a nice symbol for the constants, or for the complements.
It is just as easy to create copies or to fill planes with apzoc; apzoc("abaz") would place a copy of plane 0 in plane 2, while clearing plane 3 and leaving the other two untouched. Clearly, permitting CAM boards to perform all the work is far preferable to extracting the contents of the bitplanes, then modifying and replacing them.