RELEASED
PM4354 COMET-QUAD
DATASHEET
PMC-1990315
ISSUE 6
FOUR CHANNEL COMBINED E1/T1/J1
TRANSCEIVER / FRAMER
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC. AND FOR ITS CUSTOMERS’ INTERNAL USE
39
9.5
T1 Inband Loopback Code Detector (IBCD)
The T1 Inband Loopback Code Detection function is provided by the IBCD block. This block
detects the presence of either of two programmable INBAND LOOPBACK ACTIVATE and
DEACTIVATE code sequences in either framed or unframed data streams. Each INBAND
LOOPBACK code sequence is defined as the repetition of the programmed code in the PCM
stream for at least 5.1 seconds. The code sequence detection and timing is compatible with the
specifications defined in T1.403-1993, TA-TSY-000312, and TR-TSY-000303. LOOPBACK
ACTIVATE and DEACTIVATE code indication is provided through internal register bits. An
interrupt is generated to indicate when either code status has changed.
9.6
T1 Pulse Density Violation Detector (PDVD)
The Pulse Density Violation Detection function is provided by the PDVD block. The block detects
pulse density violations of the requirement that there be N ones in each and every time window of
8(N+1) data bits (where N can equal 1 through 23). The PDVD also detects periods of 16
consecutive zeros in the incoming data. Pulse density violation detection is provided through an
internal register bit. An interrupt is generated to signal a 16 consecutive zero event, and/or a
change of state on the pulse density violation indication.
9.7
T1 Framer (T1-FRMR)
The T1 framing function is provided by the T1-FRMR block. This block searches for the framing
bit position in the backplane receive stream. It works in conjunction with the FRAM block to
search for the framing bit pattern in the standard superframe (SF), or extended superframe (ESF)
framing formats. When searching for frame, the FRMR simultaneously examines each of the 193
(SF) or each of the 772 (ESF) framing bit candidates. The FRAM block is addressed and
controlled by the FRMR while frame synchronization is acquired.
The time required to acquire frame alignment to an error-free backplane receive stream,
containing randomly distributed channel data (i.e. each bit in the channel data has a 50%
probability of being 1 or 0), is dependent upon the framing format. For SF format, the T1-FRMR
block will determine frame alignment within 4.4 ms 99 times out of 100. For ESF format, the T1-
FRMR will determine frame alignment within 15 ms 99 times out of 100.
Once the T1-FRMR has found frame, the backplane receive data is continuously monitored for
framing bit errors, bit error events (a framing bit error in SF or a CRC-6 error in ESF), and
severely errored framing events. The T1-FRMR also detects out of frame, based on a selectable
ratio of framing bit errors.
The T1-FRMR can also be disabled to allow reception of unframed data.