DS2152
8.1.1 Simple Idle Code Insertion and Per-Channel Loopback
The first method involves using the Transmit Idle Registers (TIR1/2/3) to determine which of the 24 T1
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 24 T1 channels. If this method is
used, then the CCR4.0 control bit must be set to 0.
Each of the bit positions in the Transmit Idle Registers (TIR1/TIR2/TIR3) represents a DS0 channel in
the outgoing frame. When these bits are set to a 1, the corresponding channel will transmit the Idle Code
contained in the Transmit Idle Definition Register (TIDR). Robbed-bit signaling and Bit 7 stuffing will
occur over the programmed Idle Code unless the DS0 channel is made transparent by the Transmit
Transparency Registers.
The Transmit Idle Registers (TIRs) have an alternate function that allows them to define a Per-Channel
Loop-Back (PCLB). If the TIRFS control bit (CCR4.0) 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 T1 line. 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.
TIR1/TIR2/TIR3: TRANSMIT IDLE REGISTERS (Address=3C to 3E Hex)
[Also used for Per-Channel Loopback]
(MSB)
CH8
(LSB)
CH1
CH9
CH7
CH15
CH23
CH6
CH14
CH22
CH5
CH13
CH21
CH4
CH12
CH20
CH3
CH11
CH19
CH2
CH10
CH18
TIR1 (3C)
TIR2 (3D)
TIR3 (3E)
CH16
CH24
CH17
SYMBOL
POSITION NAME AND DESCRIPTION
CH24
TIR3.7
TIR1.0
Transmit Idle Registers.
0=do not insert the Idle Code in the TIDR into this channel
CH1
1=insert the Idle Code in the TIDR into this channel
NOTE:
If CCR4.0=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).
TIDR: TRANSMIT IDLE DEFINITION REGISTER (Address=3F Hex)
(MSB)
(LSB)
TIDR7
TIDR6
TIDR5
TIDR4
TIDR3
TIDR2
TIDR1
TIDR0
SYMBOL
POSITION NAME AND DESCRIPTION
TIDR7
TIDR0
TIDR.7
TIDR.0
MSB of the Idle Code (this bit is transmitted first)
LSB of the Idle Code (this bit is transmitted last)
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DALLAS [ DALLAS SEMICONDUCTOR ]
