DS2154
9 PER-CHANNEL CODE (IDLE) GENERATION AND LOOPBACK
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 9.1. The receive
direction is from the E1 line to the backplane and is covered in Section 9.2.
9.1 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 9.1.1, was
a feature contained in the original DS2153 while the second method, which is covered in Section 9.1.2, is
a new feature of the DS2154.
9.1.1 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 allows 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 looped back or on how many channels can
be looped back.
TIR1/TIR2/TIR3/TIR4: TRANSMIT IDLE REGISTERS (Address = 26 to 29 Hex)
(Also used for Per-Channel Loopback.)
(MSB)
(LSB)
CH1
CH8
CH7
CH15
CH23
CH31
CH6
CH14
CH22
CH30
CH5
CH13
CH21
CH29
CH4
CH12
CH20
CH28
CH3
CH11
CH19
CH27
CH2
CH10
CH18
CH26
TIR1 (26)
TIR2 (27)
TIR3 (28
TIR4 (29)
CH16
CH24
CH32
CH9
CH17
CH25
SYMBOL
POSITION
NAME AND DESCRIPTION
Transmit Idle Registers.
CH32
TIR4.7
0 = do not insert the Idle Code in the TIDR into this channel
CH1
TIR1.0
1 = insert the Idle Code in the TIDR into this channel
Note: If CCR3.5 = 1, then a 0 in the TIRs implies that channel data is to be sourced from TSER and a 1 implies that channel data is to be
sourced from the output of the receive side framer (i.e., Per-Channel Loopback; see Figure 1-1).
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ROCHESTER [ Rochester Electronics ]
