2.0 Circuit Description
CX28394/28395/28398
2.3 System Bus
Quad/x16/Octal—T1/E1/J1 Framers
64-Bit Elastic
In 64-bit Elastic mode, the slip buffer total depth is 64 bits and the initial
throughput delay is 32 bits, or one-half of the total depth. Similar to Normal
mode, Elastic mode allows the system bus to operate at any of the programmable
bus rates, independent of the line rate. The advantage of this mode over the
two-frame mode is that throughput delay is reduced from one frame to an average
of 32 bits, and the transmit multiframe can retain its alignment with respect to the
transmit data. The disadvantage of this mode is handling the full and empty buffer
conditions. In 64-bit Elastic mode, an empty or full buffer condition causes an
Uncontrolled Slip (USLIP). Unlike an FSLIP, a USLIP is of unknown size,
ranging from 1 to 256 bits of data. The USLIP status is reported in SSTAT.
Two-Frame Short
The Two-Frame Short mode combines the depth of the Normal mode with the
throughput delay of the Elastic mode. This mode begins in Elastic mode with a
32-bit initial throughput delay, and switches to Normal modes when the buffer is
empty or full; thereafter, the Two-Frame Short and Normal modes perform
identically. If the slip buffer is full (two frames) in the Two-Frame Short and
normal modes, an FSLIP is reported; thereafter, the slip buffer performs exactly
like Normal mode.
Bypass
In Bypass mode, data is clocked through TSLIP from the TSB to the XMTR
using TXCLK as selected by the TXCLK input clock mux.
2.3.5.3 Signaling Buffer
The 32-byte Transmit Signaling Buffer [TSIG; addr 120–13F] stores a single
multiframe of signaling data input from TSIGI pin and is updated as each time
slot is received in every TSB frame. Each byte offset into TSIG is a different time
slot’s signaling data: offset 0 stores TS0 signaling data, offset 1 stores TS1
signaling data, etc. The signaling data is stored in the least significant 4 bits of the
signaling buffer. Similar to TSLIP, TSIG has read/write processor access for
accessing or overwriting signaling information. TFSYNC is used by the signaling
buffer to identify the frame boundaries in the TSIGI data stream.
2.3.5.4 Transmit
Framing
A transmit framing option is provided to allow the transmitter to automatically
align to the transmit PCM data on TPCMI. In this mode, the Transmit Framer
searches transmit data for a valid E1 or T1 framing pattern. The transmit data
stream has two framing functions: offline framer and an online framer. The offline
framer recovers the transmit frame alignment (TFSYNC). The online framer
monitors the frame alignment found by the offline framer and recovers
multiframe alignment (TMSYNC).
Transmit Frame Alignment
Transmit frame resynchronization is initiated by activating the Transmit Loss
Of Frame (TLOF) status bit in the Alarm 2 status [ALM2; addr 048] register by
the online framer. The TLOF criteria is set in the TLOFA, TLOFB, and TLOFC
bits of the Transmitter Configuration register [TCR1; addr 071]. The online
framer supports the following LOF criteria for T1: 2 frame bit errors out of 4, 2
out of 5, or 2 out of 6; for E1, it supports 3 out of 3. Figure 2-19 illustrates
transmit framing and timebase alignment options.
2-36
Conexant
100054E
CONEXANT [ CONEXANT SYSTEMS, INC ]
