Datasheet

TLK110
www.ti.com
SLLS901D DECEMBER 2011REVISED JANUARY 2014
3.10 Loopback Functionality
The TLK110 provides several options for Loopback that test and verify various functional blocks within the
PHY. Enabling loopback mode allows in-circuit testing of the TLK110 digital and analog data path.
Generally, the TLK110 may be configured to one of the Near-end loopback modes or to the Far-end
(reverse) loopback.
3.10.1 Near-End Loopback
Near-end loopback provides the ability to loop the transmitted data back to the receiver via the digital or
analog circuitry. The point at which the signal is looped back is selected using loopback control bits with
several options being provided. Figure 3-7 shows the PHY near-end loopback functionality.
Figure 3-7. Block Diagram, Near-End Loopback Mode
The Near-end Loopback mode is selected by setting the respective bit in the BIST Control Register
(BISCR), MII register address 0x0016. MII loopback can be selected by using the BMCR register at
address 0x0000, bit [14].
The Near-end Loopback can be selected according to the following:
Reg 0x0000, Bit [14]: MII Loopback
Reg 0x0016, Bit [0]: PCS input Loopback
Reg 0x0016, Bit [1]: PCS output Loopback
Reg 0x0016, Bit [2]: Digital Loopback
Reg 0x0016, Bit [3]: Analog Loopback
Table 3-4 describes the available operational modes for each loop mode:
Table 3-4. Loop Modes
Loop Mode MII PCS Input PCS Output Digital Analog
(1)
External
Force 10/100 ANEG
Operational Setting Force/ANEG 100/10 Force 100/10 Force 100 Force 100 Force/ANEG 100/10
10
Operational MAC int. MII Only MII or RMII MII or RMII MII or RMII MII or RMII MII or RMII
(1) Requires 100Ω termination
While in MII Loopback mode, there is no link indication, but packets propagate back to the MAC. While in
MII Loopback mode the data is looped back, and can also be transmitted onto the media. For transmitting
data during MII loopback in 100BT only please use bit [6] in the BISCR Register address 0x0016. For
proper operation in Analog Loopback mode, attach 100Ω terminations to the RJ45 connector. External
Loopback can be performed while working in normal mode (Bits 3:0 of the BISCR register are asserted to
0, and on the RJ45 connector, pin 1 is connected to pin 3 and pin 2 is connected to pin 6). To maintain
the desired operating mode, Auto-Negotiation should be disabled before selecting Loopback mode. This
constraint does not apply for external-loopback mode. For selected loopback Delay propagation timing
please see Section 9.7.21.
Copyright © 2011–2014, Texas Instruments Incorporated Hardware Configuration 17
Submit Documentation Feedback
Product Folder Links: TLK110