AD8155

Data Sheet

Rev. A | Page 16 of 35

Table 6. Features Available Through Toggle Pin or Serial Control

Feature

Pin Control

Serial Control

Switch Features

BICAST

One pin

One bit

A/B Lane Select

Two pins

Two bits

Loopback

Three pins

Three bits

Rx Features

EQ Levels

Two settings

10 settings

N/P Swap

Not available

Available

Squelch

Enabled

Three bits

Tx Features

Programmable Output Levels

±400 mV diff fixed1

±200 mV diff/±300 mV diff/±400 mV diff/±600 mV diff

PE Levels

Two settings

>7 settings

1 ±400 mV diff indicates a 400 mV amplitude signal measured between two differential nodes. The voltage swing at differential I/O pins is described in this data sheet

both in terms of the differentially measured voltage range (±400 mV diff, for example) and in terms of peak-to-peak differential swing, denoted as mV p-p diff. An

output level setting of ±400 mV diff delivers a differential peak-to-peak output voltage of 800 mV p-p diff.

THE SWITCH

(MUX/DEMUX/UNICAST/BICAST/LOOPBACK)

The mux and demux functions of the AD8155 can be

controlled either with the toggle pins or through the register

map. The multiplexer path switches received data from Input

Port A or Input Port B to Output Port C. The SEL[1:0] pins allow

switching lanes independently. The demultiplexer path

switches received data from Input Port C to Output Port A,

Output Port B, or (if bicast mode is enabled) to both Output Port

A and Output Port B.

Table 7. Port Selection and Configuration with All

Loopbacks Disabled

BICAST

SELx

Output

Port A

Output

Port B

Output

Port C

0

0

Ix_C[1:0]

Idle

Ix_A[1:0]

0

1

Idle

Ix_C[1:0]

Ix_B[1:0]

1

0

Ix_C[1:0]

Ix_C[1:0]

Ix_A[1:0]

1

1

Ix_C[1:0]

Ix_C[1:0]

Ix_B[1:0]

When the device is in unicast mode, the output lanes on either

Port A or Port B are in an idle state. In the idle state, the

transmitter output current is set to 0, and the P and N sides of

the lane are pulled up to the output termination voltage

through the on-chip termination resistors. To save power, the

unused receiver automatically disables.

The AD8155 supports port-level loopback, illustrated in Figure 36.

The loopback control pins override the lane select (SEL[1:0])

and bicast control (BICAST) pin settings at the port level. In serial

control mode, Bits [6:4] of Register 0x01 control loopback and

are equivalent to asserting Pin LB_A, Pin LB_B, and Pin LB_C.

Table 8 summarizes the different loopback configurations.

The loopback feature is useful for system debug, self-test, and

initialization, allowing system ASICs to compare Tx and Rx

data sent over a single bidirectional link. Loopback can also be

used to configure the device as a two- to six-lane receive

equalizer or backplane redriver.