VAXBI Designer's Notebook

The "VAXBI Designer's Notebook" (EK-VBIDS-RM-001) is a confidential and proprietary guide published by Digital Equipment Corporation. Its primary purpose is to assist engineers and system architects in designing and building options for the VAXBI bus, providing practical guidance that complements the comprehensive VAXBI System Reference Manual.

The document emphasizes that Digital Equipment Corporation ensures fundamental mechanical, electrical, and logical compatibility of VAXBI systems through its standardized hardware components, most notably the Bus Interconnect Interface Chip (BIIC). This means option designers are largely freed from dealing with low-level bus protocols and signal integrity, allowing them to focus on the user interface logic and ensuring software/architectural compatibility.

Key areas covered include:

• VAXBI Design Philosophy: Outlines Digital's goals for the bus, such as high bandwidth, support for multiprocessing and caching, data integrity, and ease of maintenance.
• Design Considerations and Tips: Provides advice on architectural tradeoffs (e.g., favoring master-port-only adapter designs for simplicity and performance by leveraging BIIC's internal registers), optimizing bus bandwidth, handling interrupts, and self-test requirements.
• VAXBI Module Layout Guide: Offers detailed instructions and best practices for the physical design of VAXBI printed circuit boards. It specifies critical areas like the VAXBI Corner (where the BIIC and other bus interface components reside, with strict layout rules), connector segments, power plane configurations, and signal capacitance limitations to maintain system performance and compatibility.
• Design Examples: Presents the Instrument Control Adapter (ICA), a VAXBI to IEEE-488 and STD Bus adapter, as a case study. This example illustrates how design requirements translate into specific decisions regarding hardware components (e.g., Z80 microprocessor) and functional implementation, demonstrating a practical application of VAXBI design principles.
• Migration of Designs: Discusses the challenges of adapting older UNIBUS and Q-bus designs to the VAXBI, particularly concerning address translation and efficient data handling, emphasizing the need to utilize VAXBI's octaword transaction capabilities.
• Simulation and Debugging Tools: Introduces specialized tools like the Realchip BIIC model (for hardware simulation and verification of VAXBI designs) and the Tektronix DAS91VB (a custom logic analyzer for VAXBI bus debugging, design verification, and performance tuning). These tools are highlighted as essential due to the VAXBI's complexity and strict electrical specifications.
• Manufacturing Support: Includes information on Gerber tape and drill tape formats for PCB manufacturing, as well as details on transition header interconnects for external cabling.

In summary, the "VAXBI Designer's Notebook" serves as a comprehensive practical handbook for developers, guiding them through the intricacies of VAXBI option design from high-level architectural decisions down to precise physical layout and testing, all while leveraging Digital's pre-engineered bus interface to ensure robust system compatibility and performance.