IBM 5280 Distributed Data System - Index of

Addressing a Byte Within the PartitionTI-Ie size of the partition cannot be greater than 64 K bytes; therefore, ,my bytt::within the partition can be addressed with 16 bits (hex 0000 through FFFF). A16-bit address is stored in the third and fourth byte of an object code instruction.Example:lop Code I16-Bit Address" IHexadecimal 2461Addressing an Object Code InstructionBecause object code instructions begin on 4-byte boundaries, the last 2 bits of the16-bit address are always zeros. These 2 bits can be used for flags; the high-order14 bits are used to address the instruction. In an object code instruction, a 14-bitaddress is stored in the high-order 14 bits of the third and fourth bytes as follows:Hexadecimal 139414-Bit AddressFlag BitsInstruction 0 isplacementIn certain branch instructions, the label in the source instruction is converted to adisplacement rather than to an address. An instruction displacement is the numberof 4-byte object code instructions from the next sequential instruction to skipif the branch is taken. An instruction displacement is 8 bits long and is stored inthe fourth byte of an object code instruction. A positive displacement can causea forward jump of up to 128 object code instructions. A negative displacementis stored in the twos complement of the displacement value. A negatiye displacementcauses a backward jump of up to 128 object code instructions from theinstruction following the branch instruction.132