11001101iiiiiiii
r0 ← SignExtend32(R0);
gbr ← SignExtend32(GBR);
imm ← ZeroExtend8(i);
address ← ZeroExtend32(r0 + gbr);
value ← ZeroExtend8(ReadMemory8(address));
value ← value ∧ imm;
WriteMemory8(address, value);