DS26528_07 Datasheet, PDF (44/276 Pages) Dallas Semiconductor – Octal T1/E1/J1 Transceiver

DS26528 Octal T1/E1/J1 Transceiver
8.9 Framers
The DS26528 framer cores are software selectable for T1, J1, or E1. The receive framer locates the frame and
multiframe boundaries and monitors the data stream for alarms. It is also used for extracting and inserting signaling
data, T1 FDL data, and E1 Si- and Sa-bit information. The receive-side framer decodes AMI, B8ZS line coding,
synchronizes to the data stream, reports alarm information, counts framing/coding and CRC errors, and provides
clock/data and frame-sync signals to the backplane interface section. Diagnostic capabilities include loopbacks,
and 16-bit loop-up and loop-down code detection. The device contains a set of internal registers for host access
and control of the device.
On the transmit side, clock, data, and frame-sync signals are provided to the framer by the backplane interface
section. The framer inserts the appropriate synchronization framing patterns, alarm information, calculates and
inserts the CRC codes, and provides the B8ZS (zero code suppression) and AMI line coding.
Both the transmit and receive path have an HDLC controller. The HDLC controller transmits and receives data via
the framer block. The HDLC controller can be assigned to any time slot, portion of a time slot, or to FDL (T1). The
HDLC controller has separate 64-byte Tx and Rx FIFO to reduce the amount of processor overhead required to
manage the flow of data.
The backplane interface provides a versatile method of sending and receiving data from the host system. Elastic
stores provide a method for interfacing to asynchronous systems, converting from a T1/E1 network to a 2.048MHz,
4.096MHz, 8.192MHz, or N x 64kHz system backplane. The elastic stores also manage slip conditions
(asynchronous interface). An IBO is provided to allow multiple framers in the DS26528 to share a high-speed
backplane.
8.9.1 T1 Framing
DS1 trunks contain 24 bytes of serial voice/data channels bundled with an overhead bit, the F-bit. The F-bit
contains a fixed pattern for the receiver to delineate the frame boundaries. The F-bit is inserted once per frame at
the beginning of the transmit frame boundary. The frames are further grouped into bundles of frames 12 for D4 and
24 for ESF.
The D4 and ESF framing modes are outlined in Table 8-10 and Table 8-11. In the D4 mode, framing bit for frame
12 is ignored if Japanese Yellow is selected.
Table 8-10. D4 Framing Mode
FRAME
NUMBER
Ft
Fs
1
1
2
0
3
0
4
0
5
1
6
1
7
0
8
1
9
1
10
1
11
0
12
0
SIGNALING
A
B
44 of 276