DS2154
8.0 PER-CHANNEL CODE GENERATION
The DS2154 can replace data on a channel-by-channel basis in both the transmit and receive directions.
The transmit direction is from the backplane to the E1 line and is covered in Section 8.1. The receive
direction is from the E1 line to the backplane and is covered in Section 8.2.
8.1 TRANSMIT SIDE CODE GENERATION
In the transmit direction there are two methods by which channel data from the backplane can be
overwritten with data generated by the DS2154. The first method which is covered in Section 8.1.1 was a
feature contained in the original DS2153 while the second method which is covered in Section 8.1.2 is a
new feature of the DS2154.
8.1.1 Simple Idle Code Insertion and Per-Channel Loopback
The first method involves using the Transmit Idle Registers (TIR1/2/3/4) to determine which of the 32 E1
channels should be overwritten with the code placed in the Transmit Idle Definition Register (TIDR).
This method allows the same 8-bit code to be placed into any of the 32 E1 channels. If this method is
used, then the CCR3.5 control bit must be set to 0.
The Transmit Idle Registers (TIRs) have an alternate function that allow them to define a Per-Channel
LoopBack (PCLB). If the CCR3.5 control bit is set to 1, then the TIRs will determine which channels (if
any) from the backplane should be replaced with the data from the receive side or in other words, off of
the E1 line. See Figure 1-1. If this mode is enabled, then transmit and receive clocks and frame syncs
must be synchronized. One method to accomplish this would be to tie RCLK to TCLK and RFSYNC to
TSYNC. There are no restrictions on which channels can be loopback or on how many channels can be
looped back.
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DALLAS [ DALLAS SEMICONDUCTOR ]
