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LTC2876/LTC2877

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28767 F16

M12 PLUG

M12 SOCKET

9-PIN D-SUB

Figure 17. Connector Pin Allocations

applicaTions inForMaTion

The D-sub connector is specified for use up to 12Mbps.

Inductors are often built into the cable connectors to

reduce unwanted ringing and reflections at data rates

above1.5Mbits/s.Cableconnectorsarealsoavailablewith

termination resistors that can be switched in/out.

Table 3. Pin Designation For D-Sub and M12 Connectors.

(Connections in Bold are Mandatory)

PIN NUMBER

CONNECTION

9-PIN D-Sub

M12

1, Case

Thread

Cable Shield

GND for 24V Supply

PB (B – Red Wire)

CNTR-P

(Repeater Direction Control)

GND for Bus Termination

VCC (+5V) for Bus Termination

+24V Supply

PA (A – Green Wire)

CNTR-N

(Repeater Direction Control)

Not Used

OPERATION IN RS485 AND RS422 SYSTEMS

The LTC2876 and LTC2877 are completely compatible

with standard RS485 and RS422 networks. In these in-

stallations, the PB pin should be treated as the A pin for

compatibility with most RS485 transceivers. Likewise, the

PA pin should be matched up with the B signal in RS485.

Further discussion about this can be found in section “Bus

Pins PA and PB Naming Convention.”

Twisted pair cables with characteristic impedance of 120Ω

or 100Ω can be used. Shielded cable is recommended

for the highest electromagnetic compatibility (EMC), but

unshielded cable like CAT-5e works well. Untwisted pair

cables (UTP) should be avoided. Both ends of a cable

should be terminated differentially with resistors that

match the cable’s impedance, as illustrated in Figure 10.

Sometimes bus biasing resistors are used for non-

PROFIBUS RS485 installations to introduce a high level

(IDLE state) on the bus when nothing is driving it. An

example of such a network is shown in Figure 181. Here

the three resistors (620Ω, 130Ω, and 620Ω) replace the

single 120Ω differential resistor in one location only.

MAXIMUM PROFIBUS CABLE LENGTH

The following table gives the maximum cable segment

lengths at PROFIBUS baud rates, as specified in IEC

61158-2:

Table 2. PROFIBUS Maximum Cable Length

BAUD RATE (kbits/s)

MAX. SEGMENT LENGTH (m)

9.6

1200

19.2

1200

45.45

1200

93.75

1200

187.5

1000

500

400

1500

200

3000

100

6000

100

12000

100

CONNECTORS

The PROFIBUS standard only specifies the use of a 9-pin

D-sub connector for stations and cables. A commonly

used alternative is the 5-pin “B-coded” M12 circular con-

nectors (IEC 947-5-2). In all cases, the female side of the

connector is located in the station, while the cable uses

the male end. Connector diagrams are shown in Figure 17

and pin designations are shown in Table 3.

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