!BITS !> !CSP
!BITS ( bits addr mask -- )  
<FORTH-83>
at the cell pointed to by addr, change only the bits that are enabled in mask 
 simulate:
   : !BITS  >R 2DUP @ R NOT AND SWAP R> AND OR SWAP ! DROP ;

reference: p4_store_bits in ../src/forth-83.c:0277, export CO !BITS