ISL41334 INTERSIL [Intersil Corporation], ISL41334 Datasheet - Page 15

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

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.
ISLX1334 Advantages
.
These dual protocol ICs offer many parametric
improvements versus those offered on competing dual
protocol devices. Some of the major improvements are:
RS-232 Mode
Rx Features
RS-232 receivers invert and convert RS-232 input levels
(±3V to ±25V) to the standard TTL/CMOS levels required by
a UART, ASIC, or µcontroller serial port. Receivers are
designed to operate at faster data rates than the drivers, and
they feature very low skews (10ns) so the receivers
contribute negligibly to bit width distortion. Inputs include the
standards required 3kΩ to 7kΩ pulldown resistor, so unused
inputs may be left unconnected. Rx inputs also have built-in
hysteresis to increase noise immunity, and to decrease
erroneous triggering due to slowly transitioning input signals.
15kV Bus Pin ESD - Eases board level requirements;
2.7V Diff V
Full Failsafe RS-485 Rx - Eliminates bus biasing;
Selectable RS-485 Data Rate - Up to 20Mbps, or slew
High RS-232 Data Rate - >460kbps
Lower Tx and Rx Skews - Wider, consistent bit widths;
Lower I
Flow-Thru Pinouts - Tx, Rx bus pins on one side/logic
Smaller (SSOP and QFN) and Pb-free Packaging.
rate limited for low EMI and fewer termination issues;
pins on the other, for easy routing to connector/UART;
ISLX1334 (MASTER)
OR NC
1kΩ
CC
DY
DE
RA
OUT
- Max I
D
- Better Noise immunity and/or distance;
R
CC
GND
+5V
V
is 2-4X lower than competition;
CC
Y
Z
A
B
15
+
R
0.1µF
T
ISL81334, ISL41334
FIGURE 10. TYPICAL RS-422 NETWORK
+5V
GENERIC 422 Rx (SLAVE)
0.1µF
V
CC
RO
B
R
Rx outputs are short circuit protected, and are only tri-
statable when the entire IC is shutdown via the ON/OFF pin,
or via the active low RXEN pin available on the QFN
package option (see “ISL41334 Special Features” for more
details).
Tx Features
RS-232 drivers invert and convert the standard TTL/CMOS
levels from a UART, or µcontroller serial port to RS-232
compliant levels (±5V minimum). The Tx delivers these
compliant output levels even at data rates of 650kbps, and
with loads of 1000pF. The drivers are designed for low skew
(typically 12% of the 500kbps bit width), and are compliant to
the RS-232 slew rate spec (4 to 30V/µs) for a wide range of
load capacitances. Tx inputs float if left unconnected, and
may cause I
unused inputs to GND.
Tx outputs are short circuit protected, and incorporate a
thermal SHDN feature to protect the IC in situations of
severe power dissipation. See the RS-485 section for more
details. Drivers tri-state only in SHDN, or when the 5V power
supply is off. The SHDN function is useful for tri-stating the
outputs if both ports will always be tri-stated together (e.g.,
used as a four transceiver RS-232 port), and if it is
acceptable for the Rx to be disabled as well. A single port Tx
disable can be accomplished by switching the port to
RS-485 mode, and then using the corresponding DE pin to
tri-state the drivers. Of course, the Rx is now an RS-485 Rx,
so this option is feasible only if the Rx aren’t needed when
the Tx are disabled.
Charge Pumps
The on-chip charge pumps create the RS-232 transmitter
power supplies (typically +6/-7V) from a single supply as low
as 4.5V, and are enabled only if either port is configured for
RS-232 operation. The efficient design requires only four
RE
A
GND
CC
increases. For the best results, connect
GENERIC FULL DUPLEX 422 XCVR (SLAVE)
0.1µF
+
R
T
Y
Z
A
B
GND
+5V
V
CC
R
D
December 20, 2005
RO
DI
FN6202.1