DEC-VAXBI-AsynchronousCommsController

The DHB32 is an asynchronous communications controller designed for Digital's VAXBI systems. It allows up to sixteen terminals, modems, or serial printers to directly communicate with a VAXBI processor, connecting via a slot on the BI backplane (supporting up to four DHB32s per bus).

Key features include:

• Offloading VAX: It uses its own microprocessor and memory to manage communications lines, performing direct memory access (DMA) transfers and concurrently controlling all 16 channels with error checking, thereby reducing overhead on the VAX processor.
• Performance: Guaranteed throughput of 19,200 bps on two channels and 9,600 bps on the remaining fourteen channels simultaneously.

• Versions:

  • EIA232: Provides 16 asynchronous channels with full modem control, compliant with EIA RS-232-D.
  • DEC423: Offers 16 DECconnect channels primarily for terminal connections, plus two switchable EIA232 channels for modems.

• Compatibility: Emulates the asynchronous functions of Digital's DMB32 controller, using the same VMS driver (supported by VAX/VMS OS Version 4.6 or higher). While extending capacity from 8 to 16 asynchronous channels, it notably does not support synchronous or parallel printer channels, unlike the DMB32. It also includes comprehensive diagnostics.