5.4.6 RS485 Half Duplex Multi-point
Also referred to as “party-line”
RS485
HDPLX
RENA
RTERM
TTERM
FCTR[5]
ON
ON
ON
OFF
ON*
ON
* Terminate only if the device is the end-point of the bus.
D
ZT
R
R
R
ZT
D
D
R
D
Figure 5-9: RS485 Half Duplex Multi-Point Configuration
5.5 I/O Electrical Interface
5.5.1 ±15kV ESD Protection
The receiver inputs and transmitter outputs are characterized for ±15kV ESD protection using the
Human Body Model.
5.5.2 RS232 Transceivers
The RS232 transmitters are inverting-level translators that convert CMOS-logic levels to ±5V EIA/TIA-
232-compliant levels. The transmitters are guaranteed at a 250 kbps data rate in slew-rate limited
mode with worst-
case loads of 3kΩ in parallel with 1000pF. Data rates up to 1 Mbps can be achieved
by not asserting SLEW LIMIT. When powered down or in shutdown, the outputs are high impedance
and can be driven to ±13.2V.
The receivers convert RS232 signals to CMOS-logic output levels. All receivers have inverting outputs
that remain active in shutdown. The MAX3161E permit their receiver inputs to be driven to ±25V.
Floating receiver input signals are pulled to ground through internal 5kΩ resistors, forcing the outputs
to a logic-high.
5.5.3 RS485/RS422 Transceivers
The RS485/RS422 transceivers feature fail-safe circuitry that guarantees a logic-high receiver output
when the receiver inputs are open or shorted, or when they are connected to a terminated
transmission line with all drivers disabled. They also feature selectable reduced slew-rate drivers that
minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free data
transmission up to 250 kbps. The transmitters can operate at speeds up to 10 Mbps with the slew-rate
limiting disabled. Drivers are short-circuit current limited and thermally limited to protect them against
excessive power dissipation. Half-duplex communication is enabled by driving HDPLX high.
TPMC467 User Manual Issue 1.0.4
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