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For ESP-4 MI, ESP-8 MI and ESP-16 MI hubs, the physical interface can be changed in software,
using any of the available tools.
•
Web interface - see Displaying or Changing the Serial Port Physical Interface on page 34.
•
Configuration utility - see Displaying or Changing the Serial Port Physical Interface on
page 48.
•
Configuration file - see Port Interface Command on page 57.
Termination
When the RS-422 or RS-485 interface is enabled for a serial port, you may also enable/disable 100
ohm termination of the differential receive signal pair on that port. This termination is typically
used in RS-485 environments when the device is the first or last on a multi-drop line for a 2-wire
configuration. This termination should always be set when the hub is configured for RS-422, as this
is a point-to-point configuration.
If your configuration includes supplying your own external termination, the termination on the hub
should not be used.
On ESP-2 MI hubs, termination is enabled or disabled in hardware; see Changing the Serial Port
Interface on ESP-2 MI Hubs on page 75. On ESP-4 MI, ESP-8 MI and ESP-16 MI hubs,
termination is enabled or disabled using any of the available tools.
RS-485 transmitter and receiver transfer modes
On ESP-4 MI, ESP-8 MI and ESP-16 MI hubs, the RS-485 physical interface always uses the
ADDC (Automatic Data Detection Control) transfer mode. The transmitter is enabled and the
receiver is disabled when a space (zero) bit is sent. The transmitter is disabled and the receiver is
enabled when a mark (one) is sent. This allows rapid turnaround and release of the data pair.
On ESP-2 MI hubs, the RS-485 physical interface can use the ADDC or RTS (Request to Send)
transfer mode. In RTS mode, the transmitter is enabled and the receiver is disabled when RTS is
true. The transmitter is disabled and the receiver is enabled when RTS is false. The RS-485 transfer
mode on ESP-2 MI hubs may be specified using any of the available tools.
Serial port pin assignments
Serial port pin assignments are provided on a label on the bottom of the hub.
Table 2.3 lists the pin assignments for the RS-232 interface.
Table 2.3: RS-232 Serial Port Pin Assignments
Pin Number
1
2
3
Chapter 2: Hardware Installation and Network Configuration
RS-232
DCD
RxD
TxD
Description
Data Carrier Detect
Receive Data
Transmit Data
Direction
Input
Input
Output
7
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