23b1ce7e_SP0256_Instruction_Set__Purpose
[Register] PAGE [Size] 4 bits [Purpose] 
The PAGE register acts as a prefix, providing the upper four address bits for every JMP and JSR instruction. The PAGE register can hold any binary value from 0001 to 1111, and is set by the SETPAGE instruction. It is not possible to load it with 0000. It powers up to the value 0001, and it retains its value across JMP/JSR instructions as well as sequencer halts.
SP0256 Instruction Set
Purpose