SP302CS datasheet(6/18 Pages) SIPEX

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SIGNAL PROCESSING EXCELLENCE

isolate an SP301/302 from ground in the power-

off condition. With V

DD turned on, the transistor

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

Ω 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,

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

±7V. This identifies the

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

±200mV differential threshold voltage. Since

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”.

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