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INDUSTRIAL TEMPERATURE RANGE
IDT72V73273 3.3V TIME SLOT INTERCHANGE
DIGITAL SWITCH WITH RATE MATCHING 32,768 x 32,768 CHANNELS
DESCRIPTION (CONTINUED)
The IDT72V73273 is capable of switching up to 32,768 x 32,768 channels
without blocking. Designed to switch 64 Kbit/s PCM or N x 64 Kbit/s data, the
device maintains frame integrity in data applications and minimizes throughput
delay for voice applications on a per-channel basis.
The 64 serial input streams (RX) of the IDT72V73273 can be run at
2.048Mb/s, 4.096Mb/s, 8.192Mb/s, 16.384Mb/s or 32.768Mb/s allowing 32,
64, 128, 256 or 512 channels per 125µs frame. The data rates on the output
streams can independently be programmed to run at any of these data rates.
With two main operating modes, Processor Mode and Connection Mode, the
IDT72V73273 can easily switch data from incoming serial streams (Data
Memory) or from the controlling microprocessor via Connection Memory.
As control and status information is critical in data transmission, the Processor
Mode is especially useful when there are multiple devices sharing the input and
output streams.
With data coming from multiple sources and through different paths, data
entering the device is often delayed. To handle this problem, the IDT72V73273
has a Frame Offset feature to allow individual streams to be offset from the frame
pulse in half clock-cycle intervals up to +7.5 clock cycles.
The IDT72V73273 also provides a JTAG test access port, memory block
programming, Group Block Programming, RX/TX internal bypass, a simple
microprocessor interface and automatic ST-BUS /GCI sensing to shorten
setup time, aid in debugging and ease use of the device without sacrificing
capabilities.
FUNCTIONAL DESCRIPTION
DATA AND CONNECTION MEMORY
All data that comes in through the RX inputs go through a serial-to-parallel
conversion before being stored into internal Data Memory. The 8 KHz frame
pulse (F32i) is used to mark the 125µs frame boundaries and to sequentially
address the input channels in Data Memory.
Data output on the TX streams may come from either the serial input streams
(Data Memory) or from the Connection Memory via the microprocessor or in
the case that RX input data is to be output, the addresses in Connection Memory
are used to specify a stream and channel of the input. The Connection Memory
is setup in such a way that each location corresponds to an output channel for
each particular stream. In that way, more than one channel can output the same
data. In Processor Mode, the microprocessor writes data to the Connection
Memory locations corresponding to the stream and channel that is to be output.
The lower half (8 least significant bits) of the Connection Memory LOW is output
every frame until the microprocessor changes the data or mode of the channels.
By using this Processor Mode capability, the microprocessor can access input
and output time-slots on a per-channel basis.
The three least significant bits of the Connection Memory HIGH are used to
control per-channel mode of the output streams. The MOD2-0 bits are used to
select Processor Mode, Constant or Variable Delay Mode, Bit Error Rate, and
the High-Impedance state of output drivers. If the MOD2-0 bits are set to 1-1-1
accordingly, only that particular output channel (8 bits) will be in the High-
Impedance state. If the MOD2-0 bits are set to 1-0-0 accordingly, that particular
channel will be in Processor Mode. If the MOD2-0 bits are set to 1-0-1 a Bit Error
Rate Test pattern will be transmitted for that time slot. See BERT section. If the
MOD2-0 bits are set to 0-0-1 accordingly, that particular channel will be in
Constant Delay Mode. Finally, if the MOD2-0 bits are set to 0-0-0, that particular
channel will be in Variable Delay Mode.
SERIAL DATA INTERFACE TIMING
The master clock frequency of the IDT72V73273 is 32.768MHz, C32i. For
32.768Mb/s data rates, this results in a single-bit per clock. For 16.384Mb/s,
8.192Mb/s, 4.096Mb/s, and 2.048Mb/s this will result in two, four, eight, and
sixteen clocks per bit, respectively. The IDT72V73273 provides two different
interface timing modes, ST-BUS or GCI. The IDT72V73273 automatically
detects the polarity of an input frame pulse and identifies it as either ST-BUS
or GCI.
For 32.768Mb/s, in ST-BUS Mode, data is clocked out on a falling edge and
is clocked in on the subsequent rising-edge. For 16.384Mb/s, 8.192Mb/s,
4.096Mb/s, and 2.048Mb/s however there is not the typical associated clock
since the IDT72V73273 accepts only a 32.768MHz clock. As a result there will
be 2, 4, 8, and 16 clock between the 32.768Mb/s transmit edge and the
subsequently transmit edges. Although in this is the case, the IDT72V73273
will appropriately transmit and sample on the proper edge as if the respective
clock were present. See ST-BUS Timing for detail.
For 32.768Mb/s, in GCI Mode, data is clocked out on a rising edge and is
clocked in on the subsequent falling-edge. For 16.384Mb/s, 8.192Mb/s,
4.096Mb/s, and 2.048Mb/s however, again there is not the typical associated
clock since the IDT72V73273 accepts only a 32.768MHz clock. As a result there
will 2, 4, 8, and 16 clocks between the 32.768Mb/s transmit edge and the other
transmit edges. Although this is the case, the IDT72V73273 will appropriately
transmit and sample on the proper edge as if the respective clock were present.
See GCI Bus Timing for detail.
DELAY THROUGH THE IDT72V73273
The switching of information from the input serial streams to the output serial
streams results in a throughput delay. The device can be programmed to
perform time-slot interchange functions with different throughput delay capabilities
on a per-channel basis. For voice applications, variable throughput delay is best
as it ensure minimum delay between input and output data. In wideband data
applications, constant throughput delay is best as the frame integrity of the
information is maintained through the switch.
The delay through the device varies according to the type of throughput delay
selected in the MOD bits of the Connection Memory.
VARIABLE DELAY MODE (MOD2-0 = 0-0-0)
In this mode, mostly for voice applications where minimum throughput delay
is desired, delay is dependent on the combination of source and destination
channels. The minimum delay achievable is a 3 channel periods of the slower
data rate .
CONSTANT DELAY MODE (MOD2-0 = 0-0-1)
In this mode, frame integrity is maintained in all switching configurations by
making use of a multiple data memory buffer. Input channel data is written into
the data memory buffers during frame n will be read out during frame n+2. In
the IDT72V73273, the minimum throughput delay achievable in Constant Delay
mode will be one frame plus one channel. See Table 14.