CMOS
Functional Description
The SMX is a flexible memory module suitable for
use in the construction of timeslot interchange
circuits used in PCM voice or data switches. The
device can be configured as a data memory or a
connection memory.
The SMX has separate 16 bit input and output data
busses. A 16 bit address bus and a full
microprocessor interface is also provided.
Data is clocked into and out of the device with the
signal applied at the CK (clock) input. Depending on
the mode of operation, the memory locations for the
read or write operation can be addressed
sequentially by the internal counter or randomly via
the external address bus. A messaging sub-mode,
which permits the data latched in on the address bus
to be multiplexed on to the output data bus, is also
available (see ME pin description).
The SMX ensures integrity of the stored data by
performing a Cyclic Redundancy Check (CRC) on a
per frame basis. When a change in the memory
contents is detected from one frame to the next, the
Change Detect (CD) pin is pulled low. The output will
be reset to its normal high impedance state when DS
input is strobed while CS is low (i.e., while the device
has been selected for microprocessor access). The
CD output is not pulled low when the memory
contents have been modified by a processor access
to the device.
Modes Of Operation
The SMX can be programmed to operate in one of
eight modes as summarized in Table 1. The different
modes are used to realize specific switch
implementations. For example, to implement a 1024
channel switch, two SMXs are required. One is
operated in Data Memory mode, while the second is
operated in Connect Memory mode. A 2048 channel
switch can be realized using three SMXs. Two of the
devices are operated, alternatively, in Counter and
External modes, the third serves as the Connection
Memory.
A
detailed
description
of
the
implementation is presented in the Applications
section of this data sheet. An outline of the device
functionality in each mode is presented below.
Mode
1
2
3
4
5
6
7
8
M
X
0
0
0
0
1
1
1
1
M
Y
0
0
1
1
0
0
1
1
M
Z
0
1
0
1
0
1
0
1
Name
Data Memory - 1
Data Memory - 2
Connect Memory - 1
Connect Memory - 2
Counter Mode
External Mode
Shift Register Mode
Data Memory - 3
Abbr.
DM-1
DM-2
CM-1
CM-2
CNT
EXT
SR
DM-3
MT9080B
Data Memory Mode-1
Data Memory Mode-1 is designed for use in the
construction of a 1024 Channel Switch Matrix. Data
on the D0-D15 input bus is clocked into the SMX and
stored in memory locations addressed by the internal
11 bit counter. Data is clocked out according to the
addresses asserted on the address bus. The pin
configuration of the device in this mode is illustrated
in Figure 3
CK
Data
Input
16
FP
Data
Output
D0
i
-D15
i
D0
o
-D15
o
16
CS
DS
CD
DTA
MODE
A0-A15
ME
ODE Z
Y
Z
From Control Interface
Figure 3 - Data Memory Modes 1 and 2 Pinout
The timing for the read and write operation is
illustrated in Figure 4. The first half of each clock
period is used for precharging the internal bus. Data
is latched in and out of the device with rising edge of
the CK clock. Correct operation of the device in this
mode requires 2048 clock cycles in a single frame
defined by the frame pulse. Consequently, for
switching of 64 kbit/s PCM voice channels, the clock
frequency must be 16.384 Mbit/s with a frame rate of
8 kHz.
The address supplied on the address bus is latched
in with the first positive clock edge in a channel
timeslot. The contents of the memory location
addressed will be clocked out on D0-D15o with the
first positive clock edge in the next timeslot (see
Figure 4).
In Data Memory Mode-1, the delay through the
switch depends on the number of channel timeslots
between the input channel and the output channel. If
the time difference between the input channel and
output channel is less than two channels, data
clocked into the device in the current frame will be
clocked out in the next frame. If the difference is
greater than or equal to two channels, data will be
clocked out in the same frame.
This concept is
further illustrated in Figure 5.
2-105
Table 1. SMX Modes of Operation
MITEL [ MITEL NETWORKS CORPORATION ]
