isl81387 Intersil Corporation, isl81387 Datasheet - Page 13

• Manufacturer Part Number: isl81387
• Description: ?15kv Esd Protected, 5v, Dual Protocol Rs-232/rs-485 Transceivers
• Manufacturer: Intersil Corporation

Detailed Description
The ISL81387, ISL41387 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 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 ISL81387, ISL41387 don’t follow the RS-485
convention whereby the inverting I/O is labelled “B/Z”, and
the non-inverting I/O is “A/Y”. Thus, in the following
application diagrams, the 1387 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
*QFN ONLY,
CONNECT RXEN TO GND
Tx/Rx
ISL81387, ISL41387
ISL81387 (MASTER)
RXEN *
1kΩ
RXEN
DEN
DEN
RA
DY
RA
DY
D
D
R
R
+5V
GND
V
GND
V
+5V
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
ISL81387, ISL41387
V
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
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 9. 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- 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.
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
CC
T
GENERIC 1/2 DUPLEX 485 XCVR
+
through a 1kΩ resistor.
Y
Z
A
B
GND
+5V
V
A/Y
CC
B/Z
GND
V
+5V
CC
R
D
November 21, 2007
R
D
RO
DI
FN6201.3
RO
RE
DE
DI