MAX13170E
+5V Multiprotocol, 3Tx/3Rx, Software-
Selectable Clock/Data Transceiver
16 ______________________________________________________________________________________
Figure 18. Typical V.28 Interface
Figure 19. V.28 Termination and Internal Resistance Networks
In Figure 17, the MAX13174E is used to implement the
resistive T network that is needed to properly terminate
the V.35 driver and receiver. Internal to the MAX13174E,
S1 and S2 are closed to connect the T-network resistors
to the circuit. The V.28 termination resistor (internal
to the MAX13170E) is disabled by opening S3 to
avoid interference with the T-network impedance.
V.28 Interface
The V.28 interface is an unbalanced single-ended inter-
face (Figure 18). The V.28 driver generates a minimum
of ±5V across a 3kΩ load impedance between A’ and
C’. The V.28 receiver has a single-ended input. To aid
in rejecting system noise, the MAX13170E’s V.28
receiver has a typical hysteresis of 0.05V.
Figure 19 shows the MAX13174E’s termination
network disabled by opening S1 and S2. The
MAX13170E’s internal 5kΩ V.28 termination is enabled
by closing S3.
DTE vs. DCE Operation
Figure 20 shows a DCE or DTE controller-selectable
interface. DCE/DTE (pin 14) switches the port’s mode
of operation. See Table 1.
This application requires only one DB-25 connector,
but separate cables for DCE or DTE signal routing.
See Figure 20 for complete signal routing in DCE and
DTE modes.
