![](http://datasheet.mmic.net.cn/Maxim-Integrated-Products/DS34T102GN-_datasheet_97090/DS34T102GN-_111.png)
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For example, if the desired configuration is to ignore E1 timeslot 0 (channel 1) and timeslot 16 (channel 17), the
RBCS registers should be programmed as follows:
RBCS1 = 0x01 :: ignore E1 channel 1 ::
RBCS2 = 0x00 :: ignore E1 channel 17 ::
RBCS3 = 0x01
RBCS4 = 0xFC :: ignore E1 channels 27-32 ::
10.11 Framers
The framer cores are software selectable for E1, T1 or J1. (J1 is a variant of T1 used in Japan.) A framer, as used
the term is commonly used the telecom industry and in this document, consists of two separate pieces: the receive
framer and the transmit formatter. The receive side framer decodes AMI, HDB3 and B8ZS line coding; locates the
frame and multiframe boundaries in a received data stream; reports alarm information; counts framing, coding and
CRC errors; and provides clock, data, frame sync and optionally signaling signals to the system interface. It is also
used for extracting signaling data, T1 FDL data, and E1 Si and Sa bit information. Diagnostic capabilities include
loopbacks, and 16-bit loop-up and loop-down code detection.
On the transmit side, clock data, frame sync and optionally signaling signals are connected between the transmit
formatter and the rest of the system. The formatter inserts the appropriate framing patterns and alarm information,
calculates and inserts the CRC codes, and provides the AMI, HDB3 and B8ZS line coding. The transmit formatter
is also used for inserting signaling data, T1 FDL data, E1 Si and Sa bit information, and loop-up and loop-down
codes.
Both the receive framer and the transmit formatter have dedicated HDLC controller blocks. These may be assigned
to any timeslot or portion of a timeslot, or to the T1 ESF facilities data link (FDL). The HDLC controller has separate
64-byte Tx and Rx FIFOs to reduce the processor overhead required to manage the flow of HDLC data.
The TDM interfaces of the receive frame and transmit formatter provide flexibility in how data is sent to and
received from the host system. Elastic stores, the key element in the TDM interfaces, provide a method for
performing controlled slips when line clocks are asynchronous vs. system clocks. Elastic stores also enable DS0
mapping from an E1/T1 line to a 2.048MHz or 1.544MHz system-internal TDM data stream.
10.11.1 T1 and E1 Framing Formats
10.11.1.1 T1 Framing Formats
T1 frames contain 24 8-bit DS0 channels for voice or data plus an overhead bit called the F-bit. Over a sequence of
frames called a multiframe the F-bit values follow a fixed pattern that a receive framer can detect and use to locate
the frame and multiframe boundaries in an incoming T1 signal. The F-bit occurs once per frame at the beginning of
the frame. In most applications T1 frames are grouped into one of two types of multiframes: 12-frame superframes
(SF, also known as D4 framing) or 24-frame extended superframes (ESF). The SF and ESF framing patterns are
shown in
Table 10-34 and
Table 10-35. In the SF mode, the framing bit for frame 12 is ignored if the framer is
configured for Japanese yellow alarms
(RCR2-T1.RD4RM=1).
Table 10-36 shows the framing pattern for another
multiframe format known as SLC-96.
Table 10-34. T1-SF Framing Pattern and Signaling Bits
FRAME
NUMBER
Ft
Fs
SIGNALING
1
2
0
3
0
4
0
5
1
6
1
A
7
0