MAX13172E
+5V Multiprotocol, Software-Selectable
Clock Transceiver
14 ______________________________________________________________________________________
Applications Information
Cable-Selectable Configuration
Application
A cable-selectable, multiprotocol DTE/DCE interface is
shown in Figure 12. The mode control lines M0, M1,
and DCE/DTE are wired to the DB-25 connector. To
select the serial-interface mode, the appropriate combi-
nation of M0, M1, M2, and DCE/DTE are grounded with-
in the cable wiring. The control lines that are not
grounded are pulled high by the internal pullups on the
MAX13170E. The serial-interface protocol of the
MAX13172E is now selected based on the cable that is
connected to the DB-25 interface.
V.10 (RS-423) Interface
The V.10 interface (Figure 13) is an unbalanced single-
ended interface capable of driving a 450Ω load. The
V.10 driver generates a minimum V
O
voltage of ±4V
across A’ and C’ when unloaded and a minimum volt-
age of 0.9
V
O
when loaded with 450Ω. The V.10
receiver has a single-ended input and does not reject
common-mode differences between C and C’. The V.10
receiver input trip threshold is defined between
+250mV and -250mV with input impedance character-
istic shown in Figure 14.
The MAX13172E V.10 mode receiver has a threshold
between +50mV and +250mV. To ensure that the
receiver has proper fail-safe operation see the
Fail-Safe
section. To aid in rejecting system noise, the
MAX13172E V.10 receiver has a typical hysteresis of
25mV. Switch S3 in Figures 16a and 16b is open in
V.10 mode to disable the V.28 5kΩ termination at the
receiver input. Switch S2 is closed and switch S1 is
open to internally ground the receiver B input.
V.11 (RS-422) Interface
As shown in Figure 15, the V.11 protocol is a fully bal-
anced differential interface. The V.11 driver generates a
minimum of ±2V between nodes A and B when 100Ω
minimum resistance is presented at the load. The V.11
receiver is sensitive to differential signals of ±200mV at
receiver inputs A’ and B’. The V.11 receiver input must
comply with the impedance curve of Figure 14 and reject
common-mode signals developed across the cable
(referenced from C to C’ in Figure 15) of up to ±7V.
The MAX13172E V.11 mode receiver has a differential
threshold between -50mV and -200mV. To ensure that
the receiver has proper fail-safe operation; see the
Fail-
Safe
section. To aid in rejecting system noise, the
MAX13172E V.11 receiver has a typical hysteresis of
15mV. Switch S3 in Figure 17 is open in V.11 mode to
disable the V.28 5kΩ termination at the inverting receiv-
er input. Because the control signals are slow (60kbps),
100Ω termination resistance is generally not required for
the MAX13172E. The receiver inputs must also be com-
pliant with the impedance curve shown in Figure 14.
V.28 (RS-232) Interface
The V.28 interface is an unbalanced single-ended inter-
face (Figure 13). The V.28 generator provides a mini-
mum of ±5V across the 3kΩ load impedance between
A’ and C’. The V.28 receiver has a single-ended input.
The MAX13172E V.28 mode receiver has a threshold
between +0.8V and +2.0V. To aid in rejecting system
noise, the MAX13172E V.28 receiver has a typical hys-
teresis of 0.25V. Switch S3 in Figures 18a and 18b is
closed in V.28 mode to enable the 5kΩ V.28 termination
at the receiver inputs.
No-Cable Mode
The MAX13172E will enter no-cable mode when the
mode-select pins are left unconnected or connected
high (M0 = M1 = M2 = 1). In this mode, the multiproto-
col drivers and receivers are disabled and the supply
current is less than 10µA. The receiver outputs enter a
high-impedance state in no-cable mode, which allows
these output lines to be shared with other receiver out-
puts (the receiver outputs have an internal pullup resis-
tor to pull the outputs high if not driven). Also, in
no-cable mode, the transmitter outputs enter a high-
impedance state, so these output lines can be shared
with other devices.
DTE vs. DCE Operation
Figure 19 shows a port with one DB-25 connector that
can be configured for either DTE or DCE operation. The
configuration requires separate cables for proper signal
routing in DTE or DCE operation. Figures 20 and 21
illustrates a DCE or DTE controller-selectable interface.
The DCE/DTE and INVERT inputs switch the port’s
mode of operation (Table 1).
The MAX13170E and MAX13172E can be connected
for either DTE or DCE operation in one of two ways: a
dedicated DTE or DCE port with an appropriate gender
connector or a port with a connector that can be config-
ured for DTE or DCE operation by rerouting the signals
to the MAX13170E and MAX13172E using a dedicated
DTE cable or dedicated DCE cable. The interface mode
is selected by logic outputs from the controller or from
jumpers to either V
CC
or GND on the mode select pins.
A dedicated DCE port using a DB-25 female connector
is shown in Figure 20. Figure 21 illustrates a dedicated
DTE port using a DB-25 male connector.
