DS2148 datasheet(34/75 Pages) DALLAS

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DS2148/Q48

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INTERNAL RX TERMINATION SELECT Table 6-5

RT1

(CCR5.1)

RT0

(CCR5.0)

INTERNAL RECEIVE

TERMINATION CONFIGURATION

Internal receive-side termination disabled

Internal receive-side 120

W enabled

Internal receive-side 100

W enabled

Internal receive-side 75

W enabled

CCR6 (05H): COMMON CONTROL REGISTER 6

(MSB)

(LSB)

LLB

RLB

ARLBE

ALB

RJAB

ECRS2

ECRS1

ECRS0

SYMBOL

POSITION

DESCRIPTION

LLB

CCR6.7

Local Loopback. In Local Loopback (LLB), transmit data will

be looped back to the receive path passing through the jitter

attenuator if it is enabled. Data in the transmit path will act as

normal. See Figure 3-1 (DS2148 BLOCK DIAGRAM Figure

3-1 and section 8-2.2 for details.

0 = loopback disabled

1 = loopback enabled

RLB

CCR6.6

Remote Loopback. In Remote Loopback (RLB), data output

from the clock/data recovery circuitry will be looped back to the

transmit path passing through the jitter attenuator if it is

enabled. Data in the receive path will act as normal while data

presented at TPOS and TNEG will be ignored. See Figure 3-1

(DS2148 BLOCK DIAGRAM Figure 3-1 and section 8-2.1 for

details.

0 = loopback disabled

1 = loopback enabled

ARLBE

CCR6.5

Automatic Remote Loopback Enable and Reset. When this

bit is set high, the device will automatically go into remote

loopback when it detects loop-up code programmed into the

receive loop-up code definition registers (RUPCD1 and

RUPCD2) for a minimum of 5 seconds and it will also set the

RIR2.1 status bit. Once in a RLB state, it will remain in this

state until it has detected the loop code programmed into the

receive loop-down code definition registers (RDNCD1 and

RDNCD2) for a minimum of 5 seconds at which point it will

force the device out of RLB and clear RIR2.1. Toggling this bit

from a 1 to a 0 can reset the automatic RLB circuitry. The

action of the automatic remote loopback circuitry is logically

OR’ed with the RLB (CCR6.6) control bit (i.e., either one can

cause a RLB to occur).

ALB

CCR6.4

Analog Loopback. In analog loopback (ALB), signals at TTIP

and TRING will be internally connected to RTIP and RRING.

The incoming signals, from the line, at RTIP and RRING will

be ignored. The signals at TTIP and TRING will be transmitted

as normal. See Figure 3-1 (DS2148 BLOCK DIAGRAM

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