Figure5 - Connection Memory High Bits
}
7
6
5
4
3
BIT
2
NAME
Message
Channel
1
0
CSTo
Output
Enable
DESCRIPTION
When 1, the contents of the corresponding location in Connection
Memory Low are output on the location’s channel and stream.
When 0, the contents of the corresponding location in Connection
Memory Low act as an address for the Data Memory and so
determine the source of the connection to the location’s channel
and stream.
This bit is output on the CSTo pin one channel early. The CSTo bit
for stream 0 is output first.
If the ODE pin is high and bit 6 of the Control Register is 0, then
this bit enables the output driver for the location’s channel and
stream. This allows individual channels on individual streams to
be made high-impedance, allowing switching matrices to be
constructed. A "1" enables the driver and a "0" disables it.
If the ODE pin is low, then all serial
outputs are high-impedance. If it is high
and bit 6 in the Control Register is 1, then
all outputs are active. If the ODE pin is
high and bit 6 in the Control Register is 0,
then the bit 0 in the Connection Memory
High location enables the output drivers
for the corresponding individual ST-BUS
output stream and channel. Bit 0=1
enables the driver and bit 0=0 disables it
(see
Figure 5).
Bit 1 of each Connection Memory High
location (see
Figure 5)
is output on the
CSTo pin once every frame. To allow for
delay in any external control circuitry the
bit is output one channel before the
corresponding channel on the ST-BUS
streams, and the bit for stream 0 is output
first in the channel; e.g., bit 1’s for
channel 9 of streams 0-7 are output
synchronously with ST-BUS channel 8
bits 7-0.
Applications
Digital Switching Systems
Figures 7 and 8
show how IMP8980Ds
and MT8964s form a simple digital
switching system.
Figure 7
shows the
4
© IMP, Inc.
}
2
1
0
No Corresponding Memory
- These bits give 0s if read.
Per Channel
Control Bits
interface between the IMP8980D’s and the
filter/codecs.
Figure 8
shows the position of
these components in an example architec-
ture.
The Mitel MT8964 filter/codec in
Figure 7
receives and transmits digitized
voice signals on the ST-BUS input DR,
and ST-BUS output DX, respectively.
These signals are routed to the ST-BUS
inputs and outputs on the top IMP8980D,
which is used as a digital speech switch.
The MT8964 is controlled by the
ST-BUS input DC originating from the
bottom IMP8980D , which generates the
appropriate signals from an output channel
in Message Mode. This architecture
optimizes the messaging capability of the
line circuit by building signalling logic, e.g.,
for on-off hook detection, which commu-
nicates on an ST-BUS output. This
signalling ST-BUS output is monitored by
a microprocessor (not shown) through an
ST-BUS input on the bottom IMP8980D.
Figure 8
shows how a simple digital
switching system may be designed using the
ST-BUS architecture. This is a private
telephone network with 256 extensions
which uses a single IMP8980D as a speech
IMP8980D DS-5-00
IMP [ IMP, INC ]
