ds2156gn Maxim Integrated Products, Inc., ds2156gn Datasheet - Page 78

• Manufacturer Part Number: ds2156gn
• Description: Ds2156, Ds2156l, Ds2156ln T1/e1/j1 Single-chip Transceiver Tdm/utopia Ii Interface
• Manufacturer: Maxim Integrated Products, Inc.

12.
Register Name:
Register Description:
Register Address:
Bit #
Name
Default
Bit 0/Framer Loopback (FLB). This loopback is useful in testing and debugging applications. In FLB, the
DS2156 loops data from the transmit side back to the receive side. When FLB is enabled, the following occurs:
1)
2)
3)
Bit 1/Payload Loopback (PLB). When PLB is enabled, the following occurs:
1)
2)
3)
4)
Bit 2/Remote Loopback (RLB). In this loopback, data input by the RPOSI and RNEGI pins is transmitted back to
the TPOSO and TNEGO pins. Data continues to pass through the receive-side framer of the DS2156 as it would
normally. Data from the transmit-side formatter is ignored. See Figure 2-1 for more details.
T1 Mode: An unframed all-ones code is transmitted at TPOSO and TNEGO.
E1 Mode: Normal data is transmitted at TPOSO and TNEGO.
Data at RPOSI and RNEGI is ignored.
All receive-side signals take on timing synchronous with TCLK instead of RCLKI.
Data is transmitted from the TPOSO and TNEGO pins synchronous with RCLK instead of TCLK.
All the receive side signals continue to operate normally.
Data at the TSER, TDATA, and TSIG pins is ignored.
The TLCLK signal becomes synchronous with RCLK instead of TCLK.
LOOPBACK CONFIGURATION
Please note that it is not acceptable to have RCLK connected to TCLK during this loopback because this
causes an unstable condition.
0 = loopback disabled
1 = loopback enabled
0 = loopback disabled
1 = loopback enabled
T1 Mode. Normally, this loopback is only enabled when ESF framing is being performed but can also be
enabled in D4 framing applications. In a PLB situation, the DS2156 loops the 192 bits of payload data
(with BPVs corrected) from the receive section back to the transmit section. The FPS framing pattern,
CRC6 calculation, and the FDL bits are not looped back; they are reinserted by the DS2156.
E1 Mode. In a PLB situation, the DS2156 loops the 248 bits of payload data (with BPVs corrected) from
the receive section back to the transmit section. The transmit section modifies the payload as if it was input
at TSER. The FAS word; Si, Sa, and E bits; and CRC4 are not looped back; they are reinserted by the
DS2156.
0 = loopback disabled
1 = loopback enabled
—
7
0
—
LBCR
Loopback Control Register
4Ah
6
0
—
5
0
LIUC
4
0
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LLB
3
0
RLB
2
0
PLB
1
0
FLB
0
0