Firefox Workstation Q-Bus Adapter Module Functional Specification

This document is the Functional Specification for the Firefox Workstation Q-Bus Adapter Module (FQAM), Revision 3.0, dated December 28, 1987, by Digital Equipment Corporation.

The FQAM is an optional L-series-quad module for Firefox workstations that acts as an M-bus-to-Q-bus adapter. Only one FQAM can be present per workstation, and it must reside in M-bus slot 0.

Its core functionalities and implementation details include:

1. M-Bus Interface: Conforms to the Firefox M-Bus Specification. It allows slave access to Q-bus interface control/status registers, diagnostic ROM, and status indicators. It also enables master access to the M-bus for Q-bus Direct Memory Access (DMA) and handles interrupt generation and acknowledgement. This is primarily implemented using the Firefox Bus Interface Chip (FBIC).
2. Q-Bus Interface: Conforms to the DEC STD 160 Q22-Bus Specification. It functions solely as the Q-bus arbiter, includes a scatter/gather map to translate 4 MBytes of Q-bus memory space into the first 512 MBytes of M-bus memory, and forwards Q-bus interrupts to the M-bus. This interface uses the CVAX Q-Bus Interface Chip (CQBIC).
3. Diagnostic ROM: A 256 KByte socketed ROM is included for diagnostics and Q-bus disk/tape/network bootstrap code.
4. Status Indicators: Five (4 red, 1 green) LED indicators provide status information, which can be modified by software.
5. Clocks: The FQAM requires 10-MHz two-phase clocks for the FBIC and a 40-MHz clock for the CQBIC.
6. Safety Feature: A bus driver-disable circuit prevents damage if the module is inadvertently plugged into an incorrect slot.

The document also outlines programming guidelines, including how software locates the module, its fixed address map, the required initialization steps after a workstation reset, and restrictions (e.g., slow ROM access, and Q-bus/CQBIC access must be restricted to a single processor due to implementation constraints).