78P2352
Dual Channel
OC-3/ STM1-E/ E4 LIU
Plesiochronous Tx Serial Mode
Figure 3 represents a common condition where a
serial transmit clock is not available and/or the data
is not source synchronous to the reference clock
input. In this mode, the 78P2352 will recover a
transmit clock from the serial plesiochronous data
and bypass the internal FIFO and re-timing block.
This mode is commonly used for mezzanine cards,
modules, and any application where the reference
clock cannot always be synchronous to the transmit
source clock/data.
Reference
Clock
XO
Reference
Clock
CKREFP/N
4-bit CMOS TTL
PIx[3:0]D
PIxCK
CMIxP/N
CMI
XFMR
Coax
Framer/
Mapper
34/39 MHz
4-bit CMOS TTL
34/39 MHz
POx[3:0]D
POxCK
TDK
78P2352
RXxP/N
CMI
XFMR
Coax
Figure 4: Slave Parallel Mode
Reference
Clock
CKREFP/N
4-bit CMOS TTL
CKREFP
PIx[3:0]D
PTOxCK
CMIxP/N
CMI
XFMR
Coax
NRZ
SIxDP/N
CMIxP/N
CMI
XFMR
Coax
Framer/
Mapper
34/39 MHz
4-bit CMOS TTL
34/39 MHz
Framer/
Mapper
NRZ
140 / 155 MHz
SOxCKP/N
SOxDP/N
TDK
78P2352
RXxP/N
POx[3:0]D
POxCK
TDK
78P2352
RXxP/N
CMI
XFMR
Coax
CMI
XFMR
Coax
Figure 5: Master Parallel Mode
Figure 3: Plesiochronous; data only
(Tx CDR enabled, FIFO bypassed)
Synchronous Parallel Modes
In parallel modes, 4-bit CMOS data segments are
input to the chip with a 34.816MHz (E4
÷
4) or
38.88MHz (STM1
÷
4) synchronous clock. These
inputs are re-timed in a 4x8 clock decoupling FIFO
and then to a serializer for transmission. Because
the data is passed through the FIFO and re-timed
using a synthesized clock, the transmit nibble clock
and data
for both channels
must be source
synchronous to the provided reference clock.
For maximum compatibility with legacy ASICs, the
78P2352 can operate in both slave and master clock
modes as shown in Figures 4 and 5 respectively.
Note:
A loop-timing mode is also available to
allow external remote loopbacks (i.e. line
loopback in framer). In this mode, the FIFO is
still enabled, but the transmit data will be re-
timed using the recovered receive clock
Parallel
Mode
Slave
Slave +
*Loop-timing
Master
Transmit FIFO Description
Since the reference clock and transmit clock/data go
through different delay paths, it is inevitable that the
phase relationship between the two clocks can vary
in a bounded manner due to the fact that the
absolute delays in the two paths can vary over time.
The transmit FIFO allows long-term clock phase drift
between the Tx clock and system reference clock,
not exceeding +/- 25.6ns, to be handled without
transmit error. If the clock wander exceeds the
specified limits, the FIFO will over or under flow, and
the FERRx register signal will be asserted. This
signal can be used to trigger an interrupt. This
interrupt event is automatically cleared when a FIFO
Reset (FRSTx) pulse is applied, and the FIFO is re-
centered.
Notes:
1)
External remote loopbacks (i.e. loopback
within framer) are not possible in
synchronous operation (FIFO enabled)
unless the data is re-justified to be
synchronous to the system reference clock
or the 78P2352 is configured for loop-timing.
2)
Most E4 applications will not allow the use of
the dual channel 78P2352 as each channel
is asynchronous to each other. Teridian
recommends using the single channel
78P2351 if one cannot control the E4 timing
reference for each channel.
3)
During IC power-up or transmit power-up,
the clocks going to the FIFO may not be
stable and cause the FIFO to overflow or
underflow. As such, the FIFO should be
manually reset using FRST anytime the
transmitter is powered-up.
Rev. 2.4
HW Control Pins
SDI_PAR
High
High
High
CKMODE
Low
Float
High
SW Control Bits
PAR
1
1
1
PMODE
0
0
1
*To enable Loop-timing
SMOD[1:0]=11
in
software
mode
set
Page: 6 of 42
2006 Teridian Semiconductor Corporation
TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
