128k-Byte Processor Instruction Address Space for Each Level Status Block
Original Publication Date: 1987-Dec-01
Included in the Prior Art Database: 2005-Feb-02
This article describes a technique for a processor which provides larger than 64KB instruction address spaces while maintaining compatibility for existing 64KB instruction address spaces concurrently in the same system. Each program represented by a level status block (LSB) may fetch instructions using the entire 16-bit instruction address as a word address rather than a byte address. When Instruction Word Addressing is enabled, the instruction address space is doubled to 128KB or 64K words. In the technique disclosed herein, a bit in the level status register (LSR) bit 12, which is part of the LSB, is used to enable Instruction Word Addressing, which provides compatibility for existing programs and applications that use Instruction Byte Addressing.