sp301ct Exar Corporation, sp301ct Datasheet - Page 6

• Manufacturer Part Number: sp301ct
• Description: Rs-232/rs-422 Line Drivers/receivers
• Manufacturer: Exar Corporation

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isolate an SP301/302 from ground in the power-
off condition. With V
switch is on, connecting ground (GND) for the
device to the circuit ground. In a power-off
condition, this transistor is switched off, thus
isolating the unit from circuit ground, and thereby
leaving the driver in a high impedance state.
Multiple SP301/302s can be connected as shown
in Figure 1b.
RS-422 OPERATION
The SP301 and SP302 are fully compliant
RS-422 devices when operating in the RS-422
mode. Baud rate and drive capability have been
balanced to provide as much versatility as pos-
sible. The SP301 and SP302 are both guaran-
teed for a 1Mbps data rate, supplying 2V
minimum into a 100 load. Short circuit protec-
tion for the RS-422 operating mode is the same
as in the RS-232 mode. The driver outputs can
be shorted to ground for an infinite duration,
with a maximum current of 100mA.
The RS-422 receivers accept differential signals
at a 1Mbps rate, and translate them to a non-
inverted TTL output. The receivers are speci-
fied with a
15V differential input voltage,
DD
turned on, the transistor
which means that to operate normally, the dif-
ference betweeen the voltages at the inputs
cannot exceed 15V. The common mode volt-
age is specified as
midpoint of the range about which the differen-
tial input must lie so that the receiver can detect
a change of state. Within this 7V range, the
receivers will recognize a change in state with a
the RS-232 and RS-422 inputs are shared, all
receiver inputs are protected to 30V to guard
against inadvertently applying an RS-232 signal
to an input that is configured for RS-422. Figure
2 shows a typical circuit for the SP301/302. In
this case the SP302 is shown configured for one
(1) duplex RS-422 and two (2) duplex RS-232
communication paths.
CONFIGURING THE SP301/302
Figures 3, 5 and 6 show the various combina-
tions of simultaneous RS-232 and RS-422 op-
eration that can be achieved with the SP301.
Similarly, Figures 4, 7 and 8 show the various
combinations for the SP302. Each of these con-
figurations are software selectable by logic level
on the SELECT A and SELECT B control lines.
Configuration can be changed “on-the-fly”.
200mV differential threshold voltage. Since
7V. This identifies the
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