JAM—just another microsequencer

Abstract

JAM (Just Another Microsequencer) is a flexible - dual role microcode sequencer. It supports high performance N-Way microsequencing operations (traditional 360/370 type branch address generation techniques), along with more traditional (a la AMD 2910) sequencing control over “structured” microcode. A unique feature of the chip is that the degree of parallel branching can be changed dynamically. That is, the chip can be reconfigured to support 2-way, 4-way, … up to 256-way branching on a 14 bit Control Store address. There are 16 microsequencing operations supported including:Next Sequential Control Store Address N-Way Branch, N-Way Call and N-Way Return (Including several submodes) Conditional Branch, Conditional Call and Conditional Return Loop Control An on-chip stack provides micro-routine nesting up to 8 levels deep. The stack is also used for looping and a special conditional branching mechanism. The chip has been designed and fabricated using 4 micron NMOS technology and has a cycle time of under 100 nanoseconds.