+5V Multiprotocol, Software-Selectable
Cable Terminator
GENERATOR
50Ω
125Ω
50Ω
Figure 8. Typical V.35 Interface
BALANCED
INTERCONNECTING
CABLE
A
A′
B
B′
C
C′
LOAD
CABLE
TERMINATION
50Ω
125Ω
50Ω
RECEIVER
A′
R1
MXL1344A
52Ω
S1
S2
R3
127Ω
R2
52Ω
B′
A
R5
30kΩ
R8
5kΩ
R6
10kΩ
S3
R7
10kΩ
R4
B
30kΩ
MXL1543
RECEIVER
C′
GND
Figure 9. V.35 Termination and Internal Resistance Networks
MAX3175. With this cable wiring, the multiprotocol seri-
al port is set in RS-530A DTE mode (Table 1).
V.11 Termination
A standard V.11 interface is shown in Figure 6. For
high-speed data transmission, the V.11 specification
recommends terminating the cable at the receiver with
a 100Ω (min) resistor. The resistor, although not
required, prevents reflections from corrupting transmit-
ted data.
In Figure 7, the MXL1344A is used to terminate the V.11
receiver on the MXL1543. Internal to the MXL1344A, S1
is closed and S2 is open to present a 104Ω typical dif-
ferential resistance and high-Z common-mode imped-
ance. The MXL1543's internal V.28 termination is
disabled by opening S3.
The V.11 specification allows for signals with common-
mode variations of ±7V and differential signal ampli-
tudes from 2V to 6V with data rates as high as 10Mbps.
The MXL1344A maintains termination impedance
between 100Ω and 110Ω over these conditions.
V.35 Termination
Figure 8 shows a standard V.35 interface. The genera-
tor and the load must both present a 100Ω ±10Ω differ-
ential impedance and a 150Ω ±15Ω common-mode
impedance. The V.35 driver generates a current output
(±11mA typ) that develops an output voltage between
440mV and 660mV across the load termination net-
works.
In Figure 9, the MXL1344A is used to implement the
resistive T-network that is needed to properly terminate
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