Motorola MSC8101 ADS User's Guide Page 211

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Connect the TDM Interface to T1/E1
Multi-Channel Controllers (MCCs) 10-9
External PHY loopback. The full external Transmit-to-Receive path tests the
physical interface between the MSC8101 and the physical (PHY) device.
Figure 10-7 summarizes the three system-level loopback options: (1) SI-level internal
loopback, (2) TDM-level internal loopback, and (3) external PHY loopback.
Figure 10-7. Loopback Modes
In the absence of an external PHY, loopback modes (1) and (2) can be used, with clocks
and synchronizing signals generated by the MSC8101. The transmit and receive clocks for
TDMB are selected through the CMX SI2 Clock Route Register (CMXSI2CR); the
selected clock input pin is sourced from one of the flexible internal baud rate generator
(BRG) outputs. Frame synchronization is generated from one of the internal timers: the
timer registers are programmed to divide the BRGCLK by (32
× 8), thus creating a
positive, bit-wide pulse every 32 timeslots.
The MSC8101 has independent receive and transmit clock signals and synchronization
signals; however, making these signals common can simplify the interconnection and
synchronization. The internal loopback configurations use this concept: setting the
SI2MR[CRTx] bit internally connects the transmit clock (L1TCLK) and synchronization
(L1TSYNC) to the respective receive clock (L1RCLK) and synchronization (L1RSYNC).
In external PHY loopback mode (3), the PM6388 PHY is used. It generates separate
transmit and receive frame syncs, so the physical connection between the timer output
(TOUT) and the L1RSYNC is not used. Instead, the Ingress Frame Pulse (IFP) from the
PM6388 connects directly to the L1RSYNC in the receive direction, and the Egress Frame
Pulse (EFP) sources L1TSYNC for the transmit side. The TDM clocks between the
MSC8101 and the T1/E1 transceiver are also generated by the PM6388 with the Transmit
L1RSYNC
L1TXD
L1RXD
L1TCLK
L1RCLK
BRGx
MSC8101
TOUTy
BRG5
L1TSYNC
L1RSYNC
L1TXD
L1RXD
L1TCLK
L1RCLK
TINy
TOUTy
External pin connections
Internal connections
MCC2
L1TSYNC
SI2
TDMB
PM6388
RFSYNC
RSER
TSER
RCLK
TFSYNC
TCLK
1
3
2
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