SP3243 datasheet(9/19 Pages) SIPEX

9 / 19 page

Rev. 6/30/03

SP3238 Intelligent +3.0V to +5.5V RS-232 Transceiver

Figure 7 shows a loopback test circuit used to test

the RS-232 Drivers. Figure 8 shows the test

results of the loopback circuit with all five driv-

ers active at 120kbps with typical RS-232 loads

in parallel with 1000pF capacitors. Figure 6 shows

the test results where one driver was active at

250kbps and all five drivers loaded with an RS-

232 receiver in parallel with a 1000pF capacitor.

A solid RS-232 data transmission rate of 120kbps

provides compatibility with many designs in

personal computer peripherals and LAN appli-

cations.

Receivers

The receivers convert

±5.0V EIA/TIA-232

levels to TTL or CMOS logic output levels.

Receivers are not active when in shutdown. If

there is no activity present at the receivers for a

period longer than 100

µs during AUTO ON-

LINE® mode or when SHUTDOWN is enabled,

the device goes into a standby mode where the

circuit draws 1

µA.

The truth table logic of the driver and receiver

outputs can be found in Table 2.

The SP3238 includes an additional non-

inverting receiver with an output R1OUT. R1OUT

is an extra output that remains active and monitors

activity while the other receiver outputs are

forced into high impedance. This allows Ring

Figure 7. Loopback Test Circuit for RS-232 Driver Data

Transmission Rates

Indicator (RI) from a peripheral to be monitored

without forward biasing the TTL/CMOS inputs

of the other devices connected to the receiver

outputs.

Since receiver input is usually from a transmission

line where long cable lengths and system

interference can degrade the signal, the inputs

have a typical hysteresis margin of 300mV. This

ensures that the receiver is virtually immune to

Figure 8. Loopback Test Circuit Result at 120kbps

(All Drivers Fully Loaded)

Figure 9. Loopback Test Circuit result at 250kbps

(All Drivers Fully Loaded)

SP3238

TxIN

TxOUT

C1+

C1-

C2+

C2-

V+

V-

VCC

0.1µF

LOGIC

INPUTS

VCC

5kΩ

RxIN

RxOUT

LOGIC

OUTPUTS

SHUTDOWN

GND

VCC

ONLINE

1000pF

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