Instruction manual

FUNCTIONAL DESCRIPTION
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Physical Characteristics
The TDM bus is an 8-bit bus that snakes continuously between cabinets in a
multicabinet system as shown in Figure 3-4. The total length is about 9 feet for a
three cabinet system.
The bus is driven from any of the circuit packs in the cabinets.
Similarly, a signal on the bus can be received by any circuit pack.
Within a cabinet, the bus is printed on one side of the circuit pack carrier backplane
while the other side is solid ground. Ribbon cables are used to connect the TDM bus
between cabinets in a multi-cabinet system.
Electrical Characteristics
The TDM bus is an unbalanced, low characteristic impedance transmission line.
Paths printed over a ground plane on the carriers and the flat ribbon cables between
carriers maintain this impedance level over the full length of the bus.
One end of the bus is terminated to ground with a bus termination circuit card and
the other end is terminated by a network on the ZTN130 CPU/MEM CP. Each circuit
pack connects to the bus through a custom bus driver device. The bus driver is a
switchable constant current source so that even in the “high” output state there is no
bus loading to cause reflections. The current output of the drivers is adjusted so that
logic “high” is 1.5 volts compared to a “low” of 0 volts.
Table 3-A. TDM Bus Time Slots
Time Slot No.
Function
Time Slot No. Function
00-04
Control (5)
15
941 Hz*
16 1209 Hz*
Tones (17)
17
1336 Hz*
05
RIMS Listen
18 1447 Hz*
06
RIMS Talk
19 1637 Hz*
07
Dial Tone
20 Data Null
08 Busy Tone 21 Reorder Tone
09
Ringback Tone
10 Voice-Null 22-253 Flexible
11
Music on Hold
(232)
12 697 Hz*
13
770 Hz*
254,255
Not used (2)
14
852 Hz*
* These tones are used to generate touch-tone signals.
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