ds265188-port-t1-e1-j1-transc Maxim Integrated Products, Inc., ds265188-port-t1-e1-j1-transc Datasheet - Page 96

• Manufacturer Part Number: ds265188-port-t1-e1-j1-transc
• Description: Ds26518 8-port T1/e1/j1 Transceiver
• Manufacturer: Maxim Integrated Products, Inc.

9.12.4 Hitless Protection Switching (HPS)
Many current redundancy protection implementations use mechanical relays to switch between primary and
backup boards. The switching time in relays is typically in the milliseconds, making T1/E1 HPS impossible. The
switching event will likely cause frame-synchronization loss in any equipment downstream, affecting the quality of
service. The same is also true for tri-stating mechanisms that use software or inactive clocks for the triggering of
HPS.
The DS26518 LIUs feature fast tristatable outputs for TTIPn and TRINGn and fast disabling of internal impedance
matching for RTIPn and RRINGn within one-bit period. The TXENABLE pin is used for hitless protection circuits in
combination with the LTRCR.RHPM bit. When low, the TXENABLE pin tri-states all eight transmitters, providing a
high-impedance state on TTIPn and TRINGn. If the RHPM bit is set, the TXENABLE pin, when low, will also
disable the internal termination on RTIPn and RRINGn on a per-port basis, providing a high impedance to the
receive line.
This is a very useful function in that control can be done through a hardware pin, allowing a quick switch to the
backup system for both the receiver and the transmitter.
Figure 9-26. HPS Block Diagram
SWITCHING
CONTROL
TXENABLE
TXENABLE
PRIMARY
BACKUP
BOARD
BOARD
96 of 313
RRING
RRING
RTIP
TRING
RTIP
TRING
TTIP
TTIP
Figure 9-26
shows a typical HPS application.
DS26518 8-Port T1/E1/J1 Transceiver
INTERFACE
CARD
LINE
RX
TX