MXL1544/MAX3175
+5V Multiprotocol, Software-Selectable
Control Transceivers
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The MXL1544/MAX3175s’ mode can be selected
through software control of the M0, M1, M2, INVERT,
and DCE/DTE inputs. Alternatively, the mode can be
selected by shorting the appropriate combination of
mode control inputs to GND (the inputs left floating will
be internally pulled up to V
CC
- logic HIGH). If the M0,
M1, and M2 mode inputs are all unconnected, the
MXL1544/MAX3175 will enter no-cable mode.
Fail-Safe
The MXL1544/MAX3175 guarantee a logic HIGH
receiver output when the receiver inputs are shorted or
open, or when they are connected to a terminated
transmission line with all drivers disabled. The V.11
receiver threshold is set between -200mV and 0mV to
guarantee fail-safe operation. If the differential receiver
input voltage (B - A) is ≥ 0mV, ROUT is logic HIGH. In
the case of a terminated bus with all transmitters dis-
abled, the receiver’s differential input voltage is pulled
to 0 by the termination. With the receiver thresholds of
the MXL1544/MAX3175, this results in ROUT logic
HIGH.
The V.10 receiver threshold is set between -250mV and
0mV. If the V.10 receiver input voltage is less than or
equal to -250mV, ROUT is logic HIGH. The V.28 receiv-
er threshold is set between 0.8V and 2.0V. If the receiv-
er input voltage is less than or equal to 0.8V, ROUT is
logic HIGH. In the case of a terminated bus with trans-
mitters disabled, the receiver’s input voltage is pulled
to 0 by the termination.
Applications Information
Cable-Selectable Mode
A cable-selectable, multiprotocol DTE/DCE interface is
shown in Figure 9. The mode control lines M0, M1, and
DCE/DTE are wired to the DB-25 connector. To select
the serial interface mode, the appropriate combination
of M0, M1, M2, and DCE/DTE are grounded within the
cable wiring. The control lines that are not grounded
are pulled high by the internal pullups on the MXL1543.
The serial interface protocol of the MXL1544/MAX3175
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 10) 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 11.
The MXL1544/MAX3175 V.10 mode receiver has a dif-
ferential threshold between -250mV and +250mV. To
ensure that the receiver has proper fail-safe operation
see the Fail-Safe section. To aid in rejecting system
noise, the MXL1544/MAX3175 V.10 receiver has a typi-
cal hysteresis of 25mV. Switch S3 in Figure 12 is open
in V.10 mode to disable the V.28 5kΩ termination at the
receiver input. Switch S4 is closed and switch S5 is
open to internally ground the receiver B input.
V.11 (RS-422) Interface
As shown in Figure 13, 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 11 and
reject common-mode signals developed across the
cable (referenced from C to C’ in Figure 13) of up to
±7V.
The MXL1544/MAX3175 V.11 mode receiver has a dif-
ferential threshold between -200mV and +200mV. To
ensure that the receiver has proper fail-safe operation;
see the Fail-Safe section. To aid in rejecting system
noise, the MXL1544/MAX3175 V.11 receiver has a typi-
cal hysteresis of 15mV. Switch S3 in Figure 14 is open
in V.11 mode to disable the V.28 5kΩ termination at the
inverting receiver input. Because the control signals are
slow (60kbps), 100Ω termination resistance is generally
not required for the MXL1544/MAX3175. The receiver
inputs must also be compliant with the impedance
curve shown in Figure 11.
V.28 (RS-232) Interface
The V.28 interface is an unbalanced single-ended inter-
face (Figure 10). The V.28 generator provides a mini-
mum of ±5V across the 3kΩ load impedance between
A’ and C’. The V.28 receiver has single-ended input.
The MXL1544/MAX3175 V.28 mode receiver has a
threshold between +0.8V and +2.0V. To aid in rejecting
system noise, the MXL1544/MAX3175 V.28 receiver
has a typical hysteresis of 50mV. Switch S3 in Figure 15
is closed in V.28 mode to enable the 5kΩ V.28 termina-
tion at the receiver inputs.
No-Cable Mode
The MXL1544/MAX3175 will enter no-cable mode when
the mode-select pins are left unconnected or connect-
ed HIGH (M0 = M1 = M2 = 1). In this mode, the multi-
protocol drivers and receivers are disabled and the
