+3V to +5V
Device: SP3243E
SHUTDOWN
V+
C3
+
0.1 µF
C5
C1
+
+
0.1 µF
C1+
0.1 µF
C1-
C2+
0.1 µF
C2-
T
1
IN
V
CC
TxOUT
High-Z
Active
RxOUT
High-Z
Active
R2OUT
Active
Active
0
1
C2
+
SP3243
V-
C4
T
1
OUT
T
X
OUT
+
0.1 µF
TTL/CMOS
INPUTS
T
X
IN
R
1
OUT
TTL/CMOS
OUTPUTS
5KΩ
R
X
OUT
5KΩ
V
CC
R
1
IN
Table 2. SHUTDOWN Truth Tables
Note: In AUTO ON-LINE
®
Mode where ONLINE = GND
and SHUTDOWN = V
CC
, the device will shut down if
there is no activity present at the Receiver inputs.
R
X
IN
1000pF
1000pF
Receivers
The receivers convert +5.0V
EIA/TIA-232
levels to TTL or CMOS logic output levels. Re-
ceivers are High-Z when the AUTO ON-LINE
®
circuitry is enabled or when in shutdown. The
truth table logic of the SP3243 driver and receiver
outputs can be found in Table 2.
The SP3243E includes an additional non-in-
verting receiver with an output R
2
OUT. R
2
OUT
is an extra output that remains active and
monitors activity while the other receiver
outputs are forced into high impedance.
This allows a Ring Indicator (RI) signal from a
peripheral to be monitored without forward
biasing the TTL/CMOS inputs of the other
devices connected to the receiver outputs.
SHUTDOWN
ONLINE
To µP Supervisor
Circuit
STATUS
GND
18
Figure 11. Loopback Test Circuit for RS-232 Driver
Data Transmission Rates
Figure 12. Loopback Test results at 1Mbps
Since receiver input is usually from a transmis-
sion 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
noisy transmission lines. Should an input be left
unconnected, an internal 5KΩ pulldown resistor
to ground will commit the output of the receiver
to a HIGH state.
Figure 13. Loopback Test results at 250Kbps
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com
SP3243E_100_072309
9
EXAR [ EXAR CORPORATION ]
