The Data Hiway Interface (DHI) is implemented on two cards: 4DP7APXDH111 and 4DP7APXDH233. This two-card set provides the conversion between the parallel TTL level signals used in the Multifunction Controller, PIUs, DHP and the serial data signal levels transmitted on the Data Hiway.

The Data Hiway is a 75-Ohm coaxial cable which connects directly to the 4DP7APXDH111 card with a coax BNC connector. This card is equipped with an additional coaxial fitting and redundant circuitry to accommodate the back-up or secondary Data Hiway A and B cables. Hiway switching is automatic, i.e., the transmitter will always follow the active receiver.

The interface is data hiway driven, responding only to properly addressed data hiway Command Words and Data Words. It uses Direct Memory Access (DMA) to pass data to/from memory through dedicated RAM buffers, referred to as 'mailboxes'. Its only direct stimulus to/from the microprocessor is an interrupt to indicate that a high priority command has been placed in a mailbox.

This card has 2 LEDs, which when illuminated indicate the active Hiway, A or B.

Here is a list of all the Honeywell TDC 2000 parts tdc-2000-parts