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Multi-Service Access Device For Channelized Interfaces
Telecom Standard Product Data Sheet
Production
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-1990823, Issue 4
92
POS Receive FIFO
The Receive FIFO block contains storage capacity for 256 octets for each of the 48 possible
channels, along with management circuitry for reading and writing the FIFO. The receive FIFO
provides for the separation of the physical layer timing from the system timing.
Receive FIFO management functions include filling the receive FIFO, indicating when packets or
bytes are available to be read from the receive FIFO, maintaining the receive FIFO read and write
pointers, and detecting FIFO overrun and underrun conditions. Upon detection of an overrun, the
FIFO aborts the current packet and subsequent bytes until there is room in the FIFO. Once
enough room is available, as defined by the BT[7:0] register bit settings, the RXSDQ will wait for
the next start of packet before writing any data into the FIFO. FIFO overruns are indicated
through a maskable interrupt and register bit, and are considered a system error. A FIFO underrun
is caused when the System Interface tries to read more data words while the FIFO is empty. This
action will be detected and reported through the FUDRI interrupt, but it is not considered a
system error. The system will continue to operate normally. In that situation, RVAL can be used
by the Link Layer device to find out if valid or invalid data is provided on the System Interface.
11.17 Output Parallel TelecomBus Interface
The Output Parallel TelecomBus Interface maps payload on a SONET/SDH template of 4xSTS-
12/STM-4 or 1xSTS-48/STM-16 buses. Markers for J0/J1 byte locations are given to signal the
frame alignment. Payload and non-payload bytes are also marked appropriately. Alarm
conditions can also be indicated on the interface. The interface is clocked with the 77.76 MHz
SYSCLK. The output J0/J1 byte alignment on the parallel TelecomBus is aligned to the input
OJ0REF signal.
11.18 Output Serial TelecomBus Interface
The Output Parallel TelecomBus Interface maps payload on a SONET/SDH template of
4x777.6Mbps LVDS compatible bus. Markers for J0/J1 byte locations are given to signal the
frame alignment. Payload and non-payload bytes are also marked appropriately. Alarm
conditions can also be indicated on the interface. The output J0/J1 byte alignment on the serial
TelecomBus is referenced to the input OJ0REF signal.
11.19 DS3 Mapper (D3MA)
The DS3 Mapper (D3MA) block maps a DS3 signal into an STS-1 (STM-0/AU3) payload and
compensate for any frequency differences between the incoming DS3 serial bit rate and the
available STS-1 (STM-0/AU3) SPE mapped payload capacity. The asynchronous DS3 mapping
consists of 9 rows every 125 μs (8 KHz). Each row contains 621 information bits, 5 stuff control
bits, 1 stuff opportunity bit, and 2 overhead communication channel bits. Fixed stuff bytes are
used to fill the remaining bytes. Refer to Table 1 for a description of the DS3 mapping.