ISL41334 INTERSIL [Intersil Corporation], ISL41334 Datasheet - Page 14

• Manufacturer Part Number: ISL41334
• Manufacturer: INTERSIL [Intersil Corporation]

Typical Application
RS-232 to RS-485 Converter
The ISLX1334 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.
Tx/Rx
RS-232 OUT
RS-485 OUT
FIGURE 8. SINGLE IC RS-232 TO RS-485 CONVERTER
RxD
RS-485 IN
RS-232 IN
TxD
RXEN *
0.1µF
0.1µF
* QFN ONLY
+5V
V
NC
NC
RA
DE
DY
C
C
CC
1
2
NOTE: PINOUT FOR SOIC AND SSOP
ISLX1334
+
+
+ 0.1µF
28
27
11
10
13
12
1
2
4
5
6
7
8
D
9
SEL1
R
C1+
C1-
C2+
C2-
B1
SEL2
A1
Y1
Z1
Y2
Z2
A2
B2
5kΩ
5kΩ
GND
V
+5V
B
A
Y
Z
CC
GND
V
14
CC
D
14
26
R
R
R
ON/OFF
D
D
R
R
D
D
R
DE2 18
D
V+
A1
B1
Y1
Z1
A2
Y2
V-
+
R
3
15
24
0.1µF
25
22
23
20
19
17
T
NC
+ C
+
0.1µF
C
0.1µF
V
+5V
V
0.1µF
3
4
CC
FIGURE 9. TYPICAL HALF DUPLEX RS-485 NETWORK
CC
GENERIC 1/2 DUPLEX 485 XCVR
ISL81334, ISL41334
V
CC
RO
R
RE
B/Z
DE
Detailed Description
Each of the two ISLX1334 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 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 ISLX1334 don’t follow the RS-485
convention whereby the inverting I/O is labeled “B/Z”, and
the noninverting I/O is “A/Y”. Thus, in the application
diagrams below the 1334 A/Y (B/Z) pins connect to the B/Z
(A/Y) pins of the generic RS-485/422 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.
D
DI
A/Y
GND
0.1µF
R
T
GENERIC 1/2 DUPLEX 485 XCVR
+
A/Y
B/Z
GND
V
+5V
CC
December 20, 2005
R
D
FN6202.1
RO
RE
DE
DI