Nortel DMS-100 Series Maintenance Manual page 27

Message-waiting line circuit (NT6X19AA). Provides the features of the
type A line circuit, plus a message-waiting lamp driver circuit. When
activated, this circuit causes the message waiting lamp on the associated
telephone set to flash at 1 Hz. This action informs the subscriber that the
subscriber has a message.
Message-waiting converter (NT6X20AA). Provides –150V
synchronized pulse for the message-waiting lamp circuit. Synchronizes
from the 2.56-MHz clock pulse in the RLCM. This card must be in slot
positions 0 and 16 of the odd LSG to function correctly.
Line card type C Meridian Digital Centrex (MDC) (NT6X21AA, AB,
AC, and AD). Supports MDC-related electronic multiline telephone sets
and operator consoles.
The NT6X21AD line card provides a voice and signaling interface. The
interface is between a 2-wire, analog subscriber line and one channel of the
4-wire, 32-channel, 2.56 Mb/s bit stream of the DMS-100 Family of DMS
Systems. The card occupies one slot in the line drawer of the LCM for use
with a P-phone telephone set. This telephone set connects to the line card
with an ordinary non-loaded (NL) pair of metallic conductors. Voice and
extended signaling services that run at the same time are available on the
same loop. The transmission bandwidth on the loop consists of two
frequency bands:
1 Voice channel, 300–3400Hz
2 Signaling channel 6–10kHz. Low level signals replace normal
high-voltage signaling (ringing).
The NT6X21AD is a single line circuit line card that, with correct DIP
switch settings, is hardware backward compatible with the NT6X21AC line
card. The NT6X21AD provides enhanced features like
reduced messaging noise
Dual in-line package (DIP) switch selectable balance impedance
UDLC (universal digital loop carrier) optimized operation
DIP switch selectable (0 or –3.5dB) gain in the D/A (digital to analog)
direction
DIP switch selectable short-loop/long-loop (slp/llp), signaling levels
Feature AE1516 allows entry of the NT6X21AD cardcode, and maintenance
and diagnostics. Entry of the cardcode, and maintenance and diagnostics
occurs on the new, selectable signaling level, voice receive D/A level, and
balance impedance. The recommended DIP switch settings appear in the
following table.
DMS-100 Family RLCM Maintenance Manual XPM12 and up
Maintenance overview 1-11