10
SHM-768K
2. Introduction
2.1 General
The SHM-768K operates synchronously, full duplex over 4-wire
unconditioned lines. It has a range of 4.1 miles (6.5 km) and operates at 5
selectable rates up to 768 kbps. One of four interfaces are available: V.35,
RS-422/V.36, X.21, and RS-530. Card versions are available for V.35 and
RS-530. Applications are shown in Figures 2-1 and 2-2.
The modem uses conditioned diphase modulation (Eurocom Std. D1) to
provide immunity from background noise, eliminate normal line distortion,
and enable efficient transmission and reception of serial data over twisted-pair
cable. Transmit timing is provided internally, or derived externally from the
data terminal or from the receive signal. Receive timing is regenerated from
the received data.
The SHM-768K features V.54 diagnostic capabilities for performing local
analog loopback and remote digital loopback. The loopbacks are controlled
manually from a front-panel push-button or—for RS-530 and V.35 only—via
the DTE interface.
Pressing the front-panel push-button generates a pseudo-random test
pattern (511 bits according to CCITT V.52) for testing end-to-end
connectivity. The ERROR LED flashes for each bit error.
Figure 2-1. Point-to-Point Application.
ASM-45
ASM-45
4-wire Line
128-768 kbps
RS-530
V.35
or X.21
SHM-768K
SHM-768K
