Datasheet
11
Figure 17. Simplex Current Loop System Congurations for (a) Point-to-Point, (b) Multidrop.
and OFF states. This non-isolated active transmit-
ter provides a nominal 20 mA loop current for
the listed values of V
CC
, R2 and R3 in Figure 18.
Length of current loop (one direction) versus minimum
required DC supply voltage, V
CC
, of the circuit in Figure 18
is graphically illustrated in Figure 19. Multidrop congura-
tions will require larger V
CC
than Figure 19 predicts in order
to account for additional station terminal voltage drops.
Typical data rate performance versus distance is illustrated
in Figure 20 for the combination of a non-isolated active
transmitter and HCPL-4200 optically coupled current
loop receiver shown in Figure 18. Curves are shown for
10% and 25% distortion data rate. 10% (25%) distor-
tion data rate is dened as that rate at which 10% (25%)
distortion occurs to output bit interval with respect to
input bit interval. An input Non-Return-to-Zero (NRZ)
test waveform of 16 bits (0000001011111101) was
used for data rate distortion measurements. Data rate
is independent of current source supply voltage, V
CC
.
The cable used contained ve pairs of unshielded, twisted,
22 AWG wire (Dearborn #862205). Loop current is 20 mA
nominal. Input and output logic supply voltages are 5 V dc.
Full Duplex
The full duplex point-to-point communication of Fig-
ure 21 uses a four wire system to provide simultane-
ous, bidirectional data communication between local
and remote equipment. The basic application uses
two simplex point-to-point loops which have two
separate, active, non-isolated units at one common
end of the loops. The other end of each loop is isolated.
As Figure 21 illustrates, the combination of Avago current
loop optocouplers, HCPL-4100 transmitter and HCPL-4200