+3.3V Multiprotocol Software-Selectable

Cable Terminators and Transceivers

______________________________________________________________________________________

11

configured for V.10 or V.28 operation as a driver or

receiver (Table 3). This mode-selection table is compati-

ble for use with the MAX3170 (clock/data transceiver)

and the MAX3171/MAX3173 (control transceiver). For

example, if X.21 mode is selected in DCE mode (M2 = 0,

M1 = 1, M0 = 1, and DCE/DTE = 1), the MAX3170,

MAX3171/MAX3173, and MAX3172/MAX3174 trans-

ceivers will all be placed in X.21 DCE mode.

Fail-Safe

The MAX3172/MAX3174 guarantee a logic HIGH

receiver output when the receiver input is shorted to

GND or when it is connected to a terminated transmis-

sion line with the driver disabled. The V.10 receiver

threshold is between +25mV and +250mV. If the V.10

receiver input voltage is less than +25mV, R4OUT is

logic HIGH. If the V.10 receiver input is greater than

+250mV, R4OUT is logic LOW.

The V.28 receiver threshold is between +0.8V and

+2.0V. If the V.28 receiver input voltage is less than

+0.8V, R4OUT is logic HIGH. If the receiver input is

greater than +2.0V, R4OUT is logic LOW. If the driving

transmitter is disabled or disconnected, the receiver’s

input voltage is pulled to zero by its internal termination.

With the receiver thresholds of the MAX3172/MAX3174,

this results in a logic HIGH.

Applications Information

Older multiprotocol cable termination implementations

have been constructed using expensive relays with dis-

crete resistors, custom cables with built-in termination,

or complex circuit board configurations to route signals

to the correct termination. The MAX3172/MAX3174 pro-

vide a simple solution to this termination problem. All

required termination configurations are software selec-

table using four mode-control input pins (M2, M1, M0,

and DCE/DTE).

V.11 Termination

For high-speed data transmission, the V.11 specifica-

tion recommends terminating the cable at the receiver

100

Ω

MIN

A

′

B

′

C

′

A

B

C

GENERATOR

BALANCED

INTERCONNECTING

CABLE

CABLE

TERMINATION

RECEIVER

LOAD

Figure 6. Typical V.11 Interface

A

B

S2 OFF

V.11 MODE

V.35 MODE

HIGH-Z MODE

A

C*

B

S2 ON

S1 OFF

A

B

S2 OFF

C*

C*

*NODE C IS PROVIDED IN NETWORKS 1,2,3.

R2

52

Ω

R1

52

Ω

S1 ON

R3

127

Ω

R2

52

Ω

R1

52

Ω

S1 ON

R3

127

Ω

R2

52

Ω

R1

52

Ω

R3

127

Ω

Figure 5. MAX3172/MAX3174 Termination Network Configurations