dtj v01-02 mar1986

This issue of the Digital Technical Journal, published in March 1986, focuses on the development and architecture of the MicroVAX II System, highlighting the challenges and innovations in miniaturizing the VAX architecture to a single-chip microprocessor within a tight schedule.

The core hardware includes the MicroVAX 78032 CPU chip, which implements a subset of the VAX instruction set (microcoded for frequent instructions, emulating others). It features a fast 200ns microcycle, simplified hardware (small address translation cache, no memory cache), and parallel internal execution. The companion MicroVAX 78132 Floating Point Unit (FPU) chip provides fast floating-point calculations with three parallel datapaths and a 100ns microcycle, addressing specific electrical and signal integrity challenges. Both chips are integrated onto a carefully designed CPU board that supports synchronous memory access and Q-bus I/O.

The entire design process heavily leveraged a Custom CAD Suite for behavioral modeling, logic simulation, and layout verification, enabling rapid parallel development of hardware and software.

Software compatibility with the full VAX instruction set was a primary goal. Instructions not microcoded on the CPU are transparently handled by software emulation (macrocode) in the MicroVMS, ULTRIX-32m, and VAXELN operating systems. This involved significant work in adapting existing VAX software and developing new emulation routines, tested using a modified VAX-11/730 as a "breadboard."

The journal also details several key peripheral and system applications:

• The RQDX3 Disk Controller, designed for high-performance data transfers, utilizing a three-port data buffer and parallel internal subsystems.
• The TK50 Cartridge Tape Drive, a 100MB streaming tape drive featuring a unique auto-threading mechanism and robust error recovery for efficient backup.
• The development of the MicroVAX Workstation, focusing on the integration of graphics hardware and the User Interface Services (UIS) software for windowing and virtual displays.
• The comprehensive process of porting ULTRIX software to the MicroVAX, adapting its kernel and drivers while ensuring compatibility and minimal design changes through specific address mapping techniques.

In essence, the issue showcases Digital's success in achieving high performance, reliability, and cost-effectiveness by integrating complex VAX functionality into compact, single-chip designs, supported by advanced CAD tools and innovative software solutions.