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Signal Group
Signal Name
Type
Pin
Description
B
B_RXP
I
3
Rx, LVPECL positive signal
B_SDA
I/O
4
SDA, I2C data
B_RXN
I
5
Rx, LVPECL negative signal
B_SDP
I
7
Signal Detect, LVPECL positive signal
B_SCL
I/O
8
SCL, I2C clock
B_SDN
I
9
Signal Detect, LVPECL negative signal
B_TXEN
O
11
Tx enable
TXEN is implemented as the inverse to TXDIS
B_TXDIS
O
13
Tx disable
B_TXP
O
15
Tx, LVPECL positive signal
B_TXN
O
17
Tx, LVPECL negative signal
A
A_RXP
I
29
Rx, LVPECL positive signal
A_SDA
I/O
30
SDA, I2C data
A_RXN
I
31
Rx, LVPECL negative signal
A_SDP
I
33
Signal Detect, LVPECL positive signal
A_SCL
I/O
34
SCL, I2C clock
A_SDN
I
35
Signal Detect, LVPECL negative signal
A_TXEN
O
37
Tx enable
TXEN is implemented as the inverse to TXDIS
A_TXDIS
O
39
Tx disable
A_TXP
O
41
Tx, LVPECL positive signal
A_TXN
O
43
Tx, LVPECL negative signal
The differential signals Rx and Tx should be routed as differential pairs with a characteristic
impedance of 100 Ω differentially.
Rx Channel Design Requirements
The Rx channel is designed for an optical transceiver output that has an AC coupled 100 Ω
differential signal with 100-1000 mV amplitude, e.g. LVPECL (low voltage positive emitter
coupled logic). Each line is terminated with 50 Ω to a common point with a potential of 1.2 V on
the brick.
If a transceiver with a DC coupled output is used, series capacitors are needed to obtain desired
signal levels for the brick. Below is a figure describing three different options to connect a
transceiver output to an Rx channel on the brick:
Brick
Trans-
ceiver
Trans-
ceiver
Trans-
ceiver
Brick
Brick
AC coupled transceiver
DC coupled transceiver
DC coupled transceiver with bias current
Fig. 12
The AC coupling capacitors typically have a value of 100 nF. Resistors draining bias current
typically have a value of 150 Ω.
Anybus
®
CompactCom
™
B40 Modbus Serial User Manual
SCM-1202-130 1.1 en-US