STANDARD PRODUCT
PM4351 COMET
DATA SHEET
PMC-1970624
ISSUE 10
COMBINED E1/T1 TRANSCEIVER
The default procedure provides automatic transmission of data once a complete
packet is written. All complete packets of data will be transmitted. After the last
data byte of a packet, the CRC word (if CRC insertion has been enabled) and a
flag, or just a flag (if CRC insertion has not been enabled) is transmitted. The
TDPR then returns to the transmission of flag characters until the next packet is
available for transmission. While working in this mode, the user must only be
careful to avoid overfilling the FIFO; underruns cannot occur unless the packet is
greater than 128 bytes long. The TDPR will force transmission if the FIFO is
filled up regardless of whether or not the packet has been completely written into
the FIFO.
The second procedure transmits data only when the FIFO depth has reached a
user configured upper threshold. The TDPR will continue to transmit data until
the FIFO depth has fallen below the upper threshold and the transmission of the
last packet with data above the upper threshold has completed. In this mode,
the user must be careful to avoid overruns and underruns. An interrupt can be
generated once the FIFO depth has fallen below a user configured lower
threshold as an indicator for the user to write more data.
If there are more than five consecutive ones in the raw transmit data or in the
CRC data, a zero is stuffed into the serial data output. This prevents the
unintentional transmission of flag or abort characters.
Abort characters can be continuously transmitted at any time by setting a control
bit. During transmission, an underrun situation can occur if data is not written to
the Transmit Data Register before the previous byte of a packet currently being
transmitted has been depleted. In this case, an abort sequence is transmitted,
and the controlling processor is notified via the UDR signal.
9.23 T1 Automatic Performance Report Generation
In compliance with the ANSI T1.231, T1.403 and T1.408 standards, a
performance report is generated each second for T1 ESF applications. The
report conforms to the HDLC protocol and is inserted into the ESF facility data
link.
The performance report can only be transmitted if TDPR #1 is configured to
insert the ESF Facility Data Link and the PREN bit of the TDPR #1 Configuration
register is logic 1. The performance report takes precedence over incompletely
written packets, but it does not pre-empt packets already being transmitted.
See the Operation section for details on the performance report encoding.
PROPRIETARY AND CONFIDENTIAL
56
PMC [ PMC-SIERRA, INC ]
