ATM/SONET/SDH 155/622 Mb/s Transceiver
Mux/Demux with Integrated Clock Generation
The VSC8111 is designed to provide a SONET/SDH compliant interface between the high speed optical
networks and the lower speed User Network Interface (UNI) devices such as the PM5355 S/UNI-622 (or
PM5312 STTX). The VSC8111 transmit section converts 8 bit parallel data at 77.76 Mb/s or 19.44 Mb/s to a
serial bit stream at 622.08 Mb/s or 155.52 Mb/s, respectively. It also provides a Facility Loopback function
which loops the received high speed data and clock directly to the transmit outputs. A Clock Multiplier Unit
(CMU) is integrated into the transmit circuit to generate the high speed clock for the serial output data stream
from input references frequency of 19.44, 38.88, 51.84 or 77.76 MHz. The CMU can be bypassed by using the
receive clock in loop timing mode thus synchronizing the entire part to a single clock (RXCLKIN).
The receive section provides the serial-to-parallel conversion, converting 155 Mb/s or 622 Mb/s to an 8 bit
parallel output at 19.44 Mb/s or 77.76 Mb/s, respectively. The receive section provides an Equipment Loopback
function which will loop the low speed transmit data and clock back through the receive section to the 8 bit par-
allel data bus and clock outputs. The receive section also contains a SONET/SDH frame detector circuit which
is used to provide frame recovery in the serial to parallel converter. The block diagram on page 1 shows the
major functional blocks associated with the VSC8111.
Byte-wide data is presented to TXIN [7:0] and is clocked into the part on the rising edge of TXLSCKIN
(refer to Figure 1). The data is then serialized (MSB leading) and presented at the TXDATAOUT+/- pins.
TXDATAOUT is clocked out on the falling edge of TXCLKOUT+. The serial output stream is synchronized to
the CMU generated clock which is a phase locked and frequency scaled version of the input reference clock.
External control inputs B0-B2 and STS12 select the multiply ratio of the CMU and either STS-3 (155 Mb/s) or
STS-12 (622 Mb/s) transmission (See Table 2). A divide-by-8 version of the CMU clock (TXLSCKOUT)
should be used to synchronize the transmit interface of the UNI device to the transmit input registers on the
VSC8111. (See Application Notes, Pg. 22)
Figure 1: Data and Clock Transmit Block Diagram
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G52142-0, Rev 4.2