isl3330 Intersil Corporation, isl3330 Datasheet - Page 13

• Manufacturer Part Number: isl3330
• Description: 3.3v, ?15kv Esd Protected, Dual Protocol Rs-232/rs-485 Transceivers
• Manufacturer: Intersil Corporation

Detailed Description
The ISL333x port supports dual protocols: RS-485/RS-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 signalling, 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). 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,
see Figures 8 and 9, the 333x A/Y (B/Z) pins connect to
the B/Z (A/Y) pins of the generic RS-485/RS-422 ICs.
The 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,
*QFN ONLY,
CONNECT RXEN TO GND
Tx/Rx
ISL3330 (MASTER)
RXEN*
RXEN
1kΩ
DEN
DEN
DY
RA
RA
DY
ISL333x
D
D
R
R
GND
+3.3V
V
GND
V
+3.3V
B
A
Y
CC
Z
CC
Y
Z
A
B
13
+
+
R
R
0.1µF
0.1µF
T
T
+5V
0.1µF
FIGURE 8. TYPICAL HALF DUPLEX RS-485 NETWORK
GENERIC 1/2 DUPLEX 485 XCVR
V
ISL3330, ISL3331
FIGURE 9. TYPICAL RS-422 NETWORK
CC
RO
+5V
GENERIC 422 Rx (SLAVE)
0.1µF
R
RE
V
CC
B/Z
DE
RO
B
R
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 9. The Tx and Rx enables aren’t required,
so connect RXEN and DEN to V
Conversely, RS-485 is a true multipoint standard, which
allows up to 32 devices (any combination of drivers that 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 8. A port set to RS-485/RS-422 mode
includes one Rx and one Tx. See Application Note AN1401
for details about implementing a three pin, selectable
RS-232/half-duplex RS-485 port.
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.
A port contains two transceivers (2 Tx and 2 Rx) in RS-232
mode.
Protocol selection is handled via the 485/232 logic pin.
D
RE
A
DI
A/Y
GND
GND
GENERIC FULL DUPLEX 422 XCVR (SLAVE)
0.1µF
0.1µF
+
R
R
T
T
GENERIC 1/2 DUPLEX 485 XCVR
+
CC
Y
Z
A
B
through a 1kΩ resistor.
GND
+5V
V
A/Y
CC
B/Z
GND
V
+5V
CC
R
D
R
D
RO
DI
May 20, 2008
FN6361.0
RO
RE
DE
DI