"A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M",
"N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"

HALF-Duplex. Data flow in either direction, but not in both directions at the same time.

HDLC. High-level Data Link Control is a group of protocols for transmitting [synchronous] data Packets between Point-to-Point nodes. Data is organized into a frame in HDLC. HDLC protocol resides with Layer 2 of the OSI model, the data link layer.

HDLC Message

HIC. Heterogeneous Interconnect bus provides a bidirectional serial interconnect which builds a scalable parallel system using pairs of unidirectional lines. IEEE-1355 defines the physical and Logic Link layers between a Chip-to-Chip, Board-to-Board, or Chassis-to-Chassis interface. The HIC interface is obsolete.

HIPPI. [High-Performance Parallel Interface] The HIPPI specification defines the mechanical, electrical and signalling protocol for a high performance simplex interface [data transmits in one direction only]. An additional HPPI interface is required to transmit data in a full-duplex mode. The HIPPI interface is obsolete. HIPPI Description

HSSI. High Speed Serial Interface. The HSSI interface uses differential ECL lines to transmit data at 52Mbps out to a maximum distance of 50 feet, also EIA613.

HyperTransport. A Point-to-Point interface with at least two unidirectional links. The HyperTransport has a data rate of 800M Bytes/ps using 8 bit pairs and a 400MHz clock.