MC145425P Ver la hoja de datos (PDF) - Motorola => Freescale
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MC145425P Datasheet PDF : 16 Pages
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BACKGROUND
The MC145421 and the MC145425 ISDN UDLTs provide
an economical means of sending and receiving two B chan-
nels (64 kbps each) of voice/data and two D channels
(16 kbps each) of signal data in a two–wire configuration at
distances up to one kilometer. There are two ISDN UDLTs,
master and slave. The master UDLT is compatible with exist-
ing and evolving PABX architectures. This device transmits
2B+2D channels of data to the remote slave. At the remote
end, the slave device presents a replica of the PBX back-
plane to the terminal devices.
These devices permit existing digital PBX architectures to
remain unchanged and provide enhanced voice/data com-
munication services throughout the PBX service area by sim-
ply replacing a subscriber’s line card and telset.
All operations occur within the boundaries of an 8 kHz
frame (125 µs). In the master, the frame sequence begins on
the rising edge of MSI. In the slave, the frame begins after
the demodulation of a burst from the master. The slave initial-
izes its timing controls at this point to stay synchronized with
the master.
During one 125 µs frame four main activities are per-
formed:
1. Previously buffered 2B+2D channel data is burst to the
other end.
2. New 2B+2D channel data is accepted for the next
frame’s transmission.
3. An incoming burst is demodulated and stored.
4. 2B+2D channel data from the previous demodulated
frame is output.
The bursts are 20 bits long, composed of two 8–bit B chan-
nels and two 2–bit D channels. Bursts are encoded using a
modified DPSK method at 512 kHz. Since a single wire pair
is used, half–duplex operation is used. A 512 kHz burst is
sent from end to end in a ping–pong fashion. This method
provides apparent full–duplex 160 kbps transmission of data
at distances up to one kilometer.
GENERAL
The ISDN UDLT consists of a modulator, a demodulator,
intermediate data registers, receive and transmit data regis-
ters, and sequencing and control logic. The Rx and Tx buff-
ers interface digitally to the line card backplane signals, while
the modulator and demodulator interface to the twisted pair
transmission media. Intermediate data registers buffer data
between these main components. The ISDN UDLT is in-
tended to operate with a 5 V power supply and can be driven
by CMOS or TTL logic.
MASTER OPERATION
In the master, the rising edge of MSI initiates the 125 µs
frame. B channel data is clocked into the Rx registers under
control of TDC/RDC, RE1, and RE2. This data is combined
with the D channel data clocked in on pins D1I and D2I by the
DCLK. The resulting 20–bit packet is stored for the next
frame transmission to the slave UDLT.
The burst output to the slave consists of the 2B+2D data
loaded during the previous frame. The burst received from
the slave is demodulated and stored for outputting in the fol-
lowing frame.
MC145421•MC145425
8
B channel bits demodulated in the previous frame are out-
put on the Tx pin under control of TDC/RDC, TE1, and TE2.
Demodulated D channel bits are output on the D1O and D2O
output pins. The indication of a valid burst demodulation is
the VD output, which is updated at the start of every frame.
SLAVE OPERATION
In normal slave operation, the main synchronizing event is
completion of demodulating a burst from the master UDLT.
This action initializes the 125 µs frame boundary of the slave.
During the slave frame, B channel data is loaded and stored
under control of the BCLK, EN1, and EN2 outputs. D channel
data is loaded at D1I and D21 under control of the DCLK
output.
The demodulated burst from the master is separated into
its D channel and B channel components and output on the
D1O, D2O, and Tx pins. The return burst to the master con-
sisting of previously loaded 2B+2D data is transmitted eight
bauds after the completion of demodulation of the master’s
burst. This provides a period for line transients to diminish.
The start of the slave frame initiates two cycles of the
16 kHz DCLK, and one cycle each of the 8 kHz EN1 and EN2
enables. After completing their cycles, these outputs remain
low until another demodulation signals the start of a new
slave frame. In this manner, clock slip between the master
and slave UDLTs is absorbed each frame.
POWER–DOWN OPERATION
When PD is low in the master, the ISDN UDLT is powered
down and only that circuitry necessary to demodulate in-
coming bursts is active. No transmissions to the slave occur
during power down. If the master is receiving bursts from the
slave, the VD pin will change state upon completion of the
demodulation.
When the PD input pin is driven high, the master ISDN
UDLT is powered up. In this mode, the master bursts to the
slave every frame. B and D channel data can be loaded and
unloaded and VD is updated on the MSI rising edge.
If no bursts are received by the master, whether powered
up or not, the B channel data is unknown and the D channel
bits will remain at their last known values.
The PD pin on the slave UDLT is bidirectional with a weak
output driver that can be overdriven externally. When low,
either externally or internally derived, the slave is powered
down. No bursts to the master can be transmitted. EN1, EN2,
BCLK, and DCLK outputs are inactive during power down
except when TONE is high or a burst has been received from
the master. B and D channel data can be loaded and un-
loaded, and VD is updated upon completion of demodulation
of an incoming burst from the master. Input B and D channel
data is not transmitted until the slave is powered up, in which
case the first burst contains the most recently loaded data.
When the PD pin is high, the slave is powered up and
transmits every frame, the data enables and clocks are out-
put, and data can be loaded and unloaded.
TIME–OUT OPERATION
Time–out is an operating state in both the UDLT master
and slave devices. This state indicates that no incoming
bursts have been demodulated, forcing the VD pin low. An
internal counter is incremented for each frame that does not
contain an incoming burst. The counter is reset upon de-
modulating a burst from the far end. Time–out can occur
whether the device is powered up or down.
MOTOROLA
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