ISL33334E Datasheet, PDF (16/23 Pages) Intersil Corporation – Operates from a single 3.3V supply

ISL33334E, ISL33337E
Typical Application
RS-232 to RS-485 Converter
The ISL33334E, ISL33337E are ideal for implementing a single
IC 2-wire (Tx Data, Rx Data) protocol converter, because each
port is programmed for a different protocol. Figure 31 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
+2
28
+27
C1+
C1-
C2+
C2-
4 R1IN
5kΩ
5 R2IN
5kΩ
9, 26
V_{CC V+} 3
+
C₃
0.1µF
V- ¹⁷
R1OUT
R
24
C₄
+0.1µF
NC
R2OUT
R
25
NC
RxD
RS-232 OUT
6 T1OUT
7 T2OUT
D ^{T1IN 22}
D ^{T2IN 23}
RS-485 IN
13 B
12 A
RS-485 OUT
11 Z
10 Y
R ^{RO 18}
RE485 ¹⁶
D
DI ₂₀
DE485 ¹⁹
GND
8, 15
V_CC
NOTE: PINOUT FOR SSOP
FIGURE 31. SINGLE IC RS-232 TO RS-485 CONVERTER
Detailed Description
Each of the ISL3333XE parts supports dual protocols:
RS-485/RS-422 (port 2) and RS-232 (port 1). 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/RS-422
maximum distance of 4000’ (1220m).
RS-422 is typically a point-to-point (one driver talking to one
receiver on a bus), or a point-to-multireceiver (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 33.
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 32. Port 2 is set to RS-485 /RS-422 mode and
includes one Rx and one Tx.
RS-232 is a point-to-point, single ended (signal voltages
referenced to GND) communication protocol targeting fairly
short (<150’, 46m) and low data rate (<1Mbps) applications.
Port 1 contains two RS-232 transceivers (2 Tx and 2 Rx).
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FN8776.1
October 21, 2016