AT&T AT&T manual System Resources, Service Circuit ZTN85, Saki, On-Board, Ram

System Resources

The System Resource Circuit Packs (CP) are as follows:

●Service Circuit (ZTN85)

●Tone Detector (TN748)

●Pooled Modem (TN758).

Service Circuit (ZTN85)

The Service Circuit CP provides the clock signals of the system. It also generates and receives tones. The Service Circuit CP (Figure 3-19)consists of the following:

● Bus buffers
● Sanity and Control Interface	(SAKI)
● On-board microprocessor with	external RAM

●Clock circuit

●Tone generator

●Time slot table and counter

●Tone detector ports

●Port I/O and Sanity Check circuit.

The ZTN85 provides four touch-tone receivers, generates all tones for the system, and supplies the system clocks. The ZTN85 can support up to 75 Dual Tone Multifrequency (DTMF) dialers depending on call traffic; the TN748s might be required in heavy traffic situations, even with less than 75 DTMF dialers. Each System 25 must contain one Service Circuit CP. Power for the circuit pack (+5 volts dc) is provided on the backplane.

Bus Buffers: There are four bus buffers on the circuit pack. The clock driver and receive buffers interface three system clock signals (2.048 MHz, 8 kHz, and 160 kHz) to the TDM bus. Two buffers interface the system tones (see Table 3-A)between the TDM bus and the Service Circuit CP. Music is not provided by the Service Circuit but can be provided via a port interface on a Tip Ring Line CP (ZTN78).

SAKI: This circuit functions the same as in the SAKI in the common circuitry for the intelligent port circuits.

On-Board

Microprocessor With External RAM: This circuit functions the same as the

microprocessor in

the

common

circuitry

for the

intelligent port

circuits. In addition,

it

tells

the dual-port

RAM

in

the

time

slot

table

circuit

the appropriate

time slots in

which

to

place

a tone. The

external RAM

also

has

work

space

for complex tones (i.e., those

tones that

vary

with time).

Clock Circuit: The clock circuit consists of a 20.48-MHz oscillator, various dividers, and shift registers. The clock circuit runs independently from the rest of the Service Circuit circuitry. The clock circuits start running when the circuit pack is first powered up and is not controlled by the on-board microprocessor.

The output of the 20.48-MHz oscillator is fed to the clock divider. The divider divides by 10, 2560, and 128. These circuits produce the 2.048-MHz, 8-kHz, and 160-kHz clock signals, respectively. The clock generator feeds these signals to the clock driver/receiver bus buffer and the tone clock. The tone clock uses these signals to synchronize the counters in the tone

3-38