MT8924 Datasheet, PDF (3/14 Pages) Mitel Networks Corporation – PCM Conference Circuit (PCC) Preliminary Information

Preliminary Information
MT8924
Pin Description (continued)
Pin #
19
20
21
22
23
24
Name
F0i
Cki
Cko
DST_i
A/µ
V_SS
Description
Frame Pulse (Input). This is an 8 kHz active low input used for frame synchronization of the
PCM bit stream. The first falling edge of Cki following the falling edge of frame pulse F0i
determines the start of a new frame and must correspond to the first bit of the first channel.
When PCM frames of 1544 kbit/s are used, the rising edge of F0i must correspond to the
Extra (193rd) bit.
Clock (Input). This signal is the timing reference used for all internal operations. The PCM
bit cell boundaries lie on the alternate falling edges of this clock. The maximum allowable
clock frequency is 4096 kHz.
Clock (Output). This pin provides the master clock for a digital crosspoint switch (e.g.,
MT898x series, or the MT9080, MT9085 combination). Normally the signal on this pin is
identical to Cki. When Extra bit operating mode is selected (see Instruction 5), the first two
cycles of the master clock are suppressed (see Figure 10). This feature allows the MT8924
to operate in 1544 kbit/s systems.
ST-BUS Serial Input. This pin accepts the serial PCM input stream at a maximum allowable
bit rate of 2048 kbit/s. In normal operation the first bit of the first channel is defined by the
rising edge of Cki following the falling edge of frame pulse F0i. When Extra bit operating
mode is selected, the first bit of the first channel defines the extra bit.
A/µ - Law Select Input. When A/µ is High, A-Law is selected, and when A/µ is Low, µ-Law is
selected. The companding law selection must be done before initializing the device using
the RESET pin.
Negative Power Supply Voltage. Nominally 0 Volts.
Functional Description
The MT8924 is a device designed to provide
conferencing in a digital switching system in any
combination for up to all 32 channels of a 2048 kbit/s
ST-BUS stream (see Figure 3).
The information of channel N, frame M is first
converted to Linear PCM and then added to the
signal from other conferencees during the first half of
Microcontroller
STi0
.
.
.
.
STix-1
STix
MT8980/81/82
Digital Switch
MT8924
PCM Conference
Circuit (PCC)
STo0
.
.
.
.
STox-1
STox
channel N+1, frame M and subtracted during the
second half of channel N-1, frame M+1. After Linear-
to-PCM conversion the subtraction result goes to the
parallel-to-serial converter, and appears at the
output on the N+1 channel, M+1 frame with respect
to the corresponding sending party information (see
Figure 4).
To a microprocessor the MT8924 appears as a
memory mapped peripheral device that can be
controlled by a set of six instructions. These
commands can be used to establish or cancel
conferences between the PCM channels and also to
transmit control messages on specific operating
modes. The microprocessor can initiate and receive
status messages or check conference connections
that are currently in operation.
DSTi
Input
Information
ABC
N N+1 N+2
MT8924
Input Channels
Frame M
Output
Information
B+C A+C A+B
DSTo
N+1 N+2 N+3
Output Channels
Frame M+1
Figure 3 -Typical Conference Connection
Figure 4 - Input/Output Channel Relationship
8-5