xrt83l30 Exar Corporation, xrt83l30 Datasheet - Page 34

• Manufacturer Part Number: xrt83l30
• Description: Xrt83l30 -single-channel T1/e1/j1 Long-haul, Short-haul Line Interface Unit
• Manufacturer: Exar Corporation

XRT83L30
SINGLE-CHANNEL T1/E1/J1 LH/SH TRANSCEIVER WITH CLOCK RECOVERY AND JITTER ATTENUATOR
PROGRAMMING CONSIDERATIONS
In many applications switching the control of the transmitter outputs and the receiver line impedance to
hardware control will provide faster transmitter ON/OFF switching.
In Host Mode, there are two bits in register 18 (12H) that control the transmitter outputs and the Rx line
impedance select, TXONCNTL (Bit 5) and TERCNTL (Bit 4).
Setting bit-5 (TXONCNTL) to a “1” transfers the control of the Transmit On/Off function to the TXON Hardware
control pin (pin 58).
Setting bit-4 (TERCNTL) to a “1” transfers the control of the Rx line impedance select (RXTSEL) to the
RXTSEL Hardware control pin (pin 44).
Either mode works well with redundancy applications. The user can determine which mode has the fastest
switching time for a unique application.
TYPICAL REDUNDANCY SCHEMES
1:1 REDUNDANCY
A 1:1 facility protection redundancy scheme has one backup card for every primary card. When using 1:1
redundancy, the backup card has its transmitters tri-stated and its receivers in high impedance. This eliminates
the need for external relays and provides one bill of materials for all interface modes of operation. The transmit
and receive sections of the LIU device are described separately.
1+1 REDUNDANCY
A 1+1 line protection redundancy scheme has one backup card for every primary card, and the receivers on
the backup card are monitoring the receiver inputs. Therefore, the receivers on both cards need to be active.
The transmit outputs require no external resistors. The transmit and receive sections of the LIU device are
described separately.
TRANSMIT 1:1 & 1+1 REDUNDANCY
For 1:1 and 1+1 redundancy, the transmitters on the primary and backup card should be programmed for
Internal Impedance mode. The transmitters on the backup card should be tri-stated. Select the appropriate
impedance for the desired mode of operation, T1/E1/J1. A 0.68uF capacitor is used in series with TTIP for
blocking DC bias. See
redundancy scheme.
N
OTE
■
■
■
: For simplification, the over voltage protection circuitry was omitted.
·1:1 One backup card for every primary card (Facility Protection)
·1+1 One backup card for every primary card (Line Protection)
·N+1One backup card for N primary cards
Figure 16
for a simplified block diagram of the transmit section for 1:1 and 1+1
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REV. 1.0.1