6
FN3020.7
July 28, 2005
minimum of 300
with ±2V applied to the outputs and VCC =
0V.
Receivers
The receiver inputs accept up to
±30V while presenting the
required 3k
to 7k input impedance even it the power is off
(VCC = 0V). The receivers have a typical input threshold of
1.3V which is within the
±3V limits, known as the transition
region, of the RS-232 specification. The receiver output is
0V to VCC. The output will be low whenever the input is
greater than 2.4V and high whenever the input is floating or
driven between +0.8V and -30V. The receivers feature 0.5V
hysteresis to improve noise rejection.
Applications
The ICL232 may be used for all RS-232 data terminal and
communication links. It is particularly useful in applications
where
±12V power supplies are not available for
conventional RS-232 interface circuits. The applications
presented represent typical interface configurations.
A simple duplex RS-232 port with CTS/RTS handshaking is
illustrated in Figure 10. Fixed output signals such as DTR
(data terminal ready) and DSRS (data signaling rate select)
is generated by driving them through a 5k
resistor
connected to V+.
In applications requiring four RS-232 inputs and outputs
(Figure 11), note that each circuit requires two charge pump
capacitors (C1 and C2) but can share common reservoir
capacitors (C3 and C4). The benefit of sharing common
reservoir capacitors is the elimination of two capacitors and
the reduction of the charge pump source impedance which
effectively increases the output swing of the transmitters.
TOUT
V- < VTOUT < V+
300
400k
TXIN
GND < TXIN < VCC
V-
V+
VCC
FIGURE 7. TRANSMITTER
ROUT
GND < VROUT < VCC
5k
RXIN
-30V < RXIN < +30V
GND
VCC
FIGURE 8. RECEIVER
T1IN, T2IN
VOH
VOL
tPLH
tPHL
Average Propagation Delay =
tPHL + tPLH
2
OR
R1IN, R2IN
T1OUT, T2OUT
OR
R1OUT, R2OUT
FIGURE 9. PROPAGATION DELAY DEFINITION
-
+
-
+
-
+
CTR (20) DATA
TERMINAL READY
DSRS (24) DATA
SIGNALING RATE
RS-232
INPUTS AND OUTPUTS
TD (2) TRANSMIT DATA
RTS (4) REQUEST TO SEND
RD (3) RECEIVE DATA
CTS (5) CLEAR TO SEND
SIGNAL GROUND (7)
15
8
13
7
14
16
-
+
6
R2
R1
T2
T1
9
12
10
11
4
5
3
1
ICL232
C1
1
F
C2
1
F
TD
RTS
RD
CTS
SELECT
+5V
INPUTS
OUTPUTS
TTL/CMOS
C3
1
F
C4
1
F
2
5k
5k
FIGURE 10. SIMPLE DUPLEX RS-232 PORT WITH CTS/RTS
HANDSHAKING
ICL232