CXA16/CXB16 Technical Manual

This document is the CXA16/CXB16 Technical Manual, providing comprehensive reference information for the CXA16 and CXB16 asynchronous multiplexers developed by Digital Equipment Corporation.

The manual covers:

1. Overview & Specifications:

   • Purpose: Describes the CXA16/CXB16 as a serial-line interface providing 16 full-duplex asynchronous data channels for BA213/BA214-based Q-bus systems.
   • Modes: Operates in two programming modes (DHV11 and DHU11, with DHU11 being preferred).
   • Connectivity: CXA16 supports DEC423 connections, CXB16 supports DEC422 connections (both are data-leads-only implementations of RS-4xx-A standards, not intended for modems or Wide Area Network equipment, and modem control signals are not supported).
   • Performance: Capable of 50,000 characters per second throughput, with individually programmable transmit and receive baud rates.
   • Features: Includes a 256-entry FIFO buffer for received characters, automatic XON/XOFF flow control, self-test capabilities, and background monitor testing.

2. Installation:

   • Details the process of unpacking, inspecting, and preparing the module.
   • Explains how to set the device's Q-bus base address, interrupt vector, and programming mode using on-board switchpacks.
   • Provides guidance on bus continuity and initial installation testing using diagnostics and loopback connectors.

3. Programming:

   • Describes the CXA16/CXB16's control registers and their bit definitions (e.g., CSR, RBUF, TXCHAR, RXTIMER, LPR).
   • Outlines programming features such as initialization sequences, configuration settings, data transmission (programmed I/O and DMA), reception, interrupt control, and automatic XON/XOFF management.
   • Includes programming examples and details on diagnostic codes.

4. Troubleshooting:

   • Offers procedures to isolate communication problems, distinguishing between module, terminal, or cabling issues.
   • Covers internal diagnostics (self-test, Background Monitor Program) and external diagnostics for MicroPDP-11 and MicroVAX II systems, including various test summaries and the use of loopback connectors (H3101, H3103).
   • Lists Field-Replaceable Units (FRUs) for maintenance.

5. Technical Description:

   • Provides a detailed breakdown of the CXA16/CXB16's functional blocks, including the RAM (for transmit/receive FIFOs and control registers), OCTART chips (UARTs, baud-rate generators), and the Control Chip (housing sequencers for Q-bus interface, DMA, data I/O, self-test, and RAM arbitration).
   • Explains the internal data flow for both character reception and transmission.

The document serves as a comprehensive guide for anyone involved in the installation, configuration, programming, and maintenance of the CXA16/CXB16 asynchronous multiplexers.