ISL3332 Datasheet, PDF (14/26 Pages) Intersil Corporation – 3.3V, ±15kV ESD Protected, Two Port, Dua Protocol RS-232/RS-485 Transceivers

ISL3332, ISL3333
Typical Application
RS-232 to RS-485 Converter
The ISL3332, ISL3333 are ideal for implementing a single IC
2-wire (Tx Data, Rx Data) protocol converter, because each
port can be programmed for a different protocol. Figure 8
illustrates the simple connections to create a single
transceiver RS-232 to RS-485 converter. Depending on the
RS-232 data rate, using an RS-422 bus as an RS-232
“extension cord” can extend the transmission distance up to
4000’ (1220m). A similar circuit on the other end of the cable
completes the conversion to/from RS-232.
+3.3V
C₁
0.1µF
C₂
0.1µF
NC
TxD
RS-232 IN
+ _0.1µF
1
+
C1+
2
28
+27
C1-
C2+
C2-
26
V_CC
4 A1
R
5kΩ
5 B1
R
5kΩ
3
V+
+C3
0.1µF
V- ¹⁵ C4
+0.1µF
R_{A1 24 NC}
R_{B1 25}
NC
RxD
RS-232 OUT
V_CC
6 Y1
7 Z1
8
SEL1
9
SEL2
D ^{DY1 22}
D ^{DZ1 23}
ON/OFF ²⁰ V_CC
RS-485 IN
13 A2
12 B2
R ^{RA2 17}
RS-485 OUT
11 Y2
10 Z2
D
GND
14
D_{Y2 19}
DE2 ¹⁸
V_CC
NOTE: PINOUT FOR SSOP
FIGURE 8. SINGLE IC RS-232 TO RS-485 CONVERTER
Detailed Description
Each of the two ISL333X ports supports dual protocols:
RS-485/422, and RS-232. RS-485 and RS-422 are differential
(balanced) data transmission standards for use in high speed
(up to 20Mbps) networks, or long haul and noisy
environments. The differential signaling, coupled with
RS-485’s requirement for an extended common mode range
(CMR) of +12V to -7V make these transceivers extremely
tolerant of ground potential differences, as well as voltages
induced in the cable by external fields. Both of these effects
are real concerns when communicating over the RS-485/422
maximum distance of 4000’ (1220m). It is important to note
that the ISL333X don’t follow the RS-485 convention
whereby the inverting I/O is labeled “B/Z”, and the non
inverting I/O is “A/Y”. Thus, in the application diagrams
below the 333X A/Y (B/Z) pins connect to the B/Z (A/Y)
pins of the generic RS-485/RS-422 ICs.
RS-422 is typically a point-to-point (one driver talking to one
receiver on a bus), or a point-to-multipoint (multidrop)
standard that allows only one driver and up to 10 receivers
on each bus. Because of the one driver per bus limitation,
RS-422 networks use a two bus, full duplex structure for
bidirectional communication, and the Rx inputs and Tx
outputs (no tri-state required) connect to different busses, as
shown in Figure 10.
Conversely, RS-485 is a true multipoint standard, which
allows up to 32 devices (any combination of drivers- must be
tri-statable - and receivers) on each bus. Now bidirectional
communication takes place on a single bus, so the Rx inputs
and Tx outputs of a port connect to the same bus lines, as
shown in Figure 9. Each port set to RS-485 /422 mode
includes one Rx and one Tx.RS-232 is a point-to-point,
singled ended (signal voltages referenced to GND)
communication protocol targeting fairly short (<150’, 46m)
and low data rate (<1Mbps) applications. Each port contains
two transceivers (2 Tx and 2 Rx) in RS-232 mode. Protocol
selection is handled via a logic pin (SELX) for each port.
+3.3V
ISL333X
RA
RXEN *
Tx/Rx
DE
DY
V_CC
RB
A
Y
D
Z
GND
* QFN ONLY
GENERIC 1/2 DUPLEX 485 XCVR
RO RE DE DI
0.1µF
+
0.1µF
R
+5V
V_CC
D
B/Z
GND
A/Y
R_T
GENERIC 1/2 DUPLEX 485 XCVR
+5V
+
0.1µF
V_CC
RO
R
RE
B/Z
A/Y
DE
DI
D
R_T
GND
FIGURE 9. TYPICAL HALF DUPLEX RS-485 NETWORK
14
FN6362.0
May 27, 2008