13

LTC2844

sn2844 2844fs

V.11 (RS422) Interface

A typical V.11 balanced interface is shown in Figure 14. A

V.11 differential generator with outputs A and B with

ground C is connected to a differential receiver with

ground C

V.11 interface has a differential termination at the receiver

end that has a minimum value of 100

Ω. The termination

resistor is optional in the V.11 specification, but for the

high speed clock and data lines, the termination is required

to prevent reflections from corrupting the data. The

receiver inputs must also be compliant with the imped-

ance curve shown in Figure 12.

In V.11 mode, all switches are off except S1 of the

LTC2846’s receivers which connects a 103

Ω differential

termination impedance to the cable as shown in Figure

termination other than its V.11 receivers’ 30k input imped-

ance is necessary.

Figure 15. V.11 Receiver Configuration

AA

'

B

C

B

'

C

'

GENERATOR

BALANCED

INTERCONNECTING

CABLE

LOAD

CABLE

TERMINATION

RECEIVER

100

Ω

MIN

2844 F14

V.28 (RS232) Interface

A typical V.28 unbalanced interface is shown in Figure 16.

A V.28 single-ended generator output A with ground C is

connected to a single-ended receiver with input A

nected to A, ground C

ground C.

In V.28 mode all switches are off except S3 inside the

LTC2846/LTC2844 which connects a 6k (R8) impedance

to ground in parallel with 20k (R5) plus 10k (R6) for a

combined impedance of 5k as shown in Figure 17. The

noninverting input is disconnected inside the LTC2846/

LTC2844 receiver and connected to a TTL level reference

voltage for a 1.4V receiver trip point.

AA

'

CC

'

GENERATOR

BALANCED

INTERCONNECTING

CABLE

LOAD

CABLE

TERMINATION

RECEIVER

2844 F16

Figure 14. Typical V.11 Interface

R5

20k

LTC2844

RECEIVER

2844 F17

A

'

B

'

C

'

R8

6k

S3

R6

10k

R7

10k

GND

R4

20k

Figure 17. V.28 Receiver Configuration

Figure 16. Typical V.28 Interface

networks on the LTC2846 can be treated identically if it is assumed that an S1 switch exists and is

always closed on the R2 and R3 receivers.

R3

124

Ω

R5

20k

LTC2846

RECEIVER

2844 F15

A

'

B

'

C

'

R1

51.5

Ω

R8

6k

S2

S3

R2

51.5

Ω

R6

10k

R7

10k

GND

R4

20k

S1