XLR PRO operational design
XLR PRO Radio Frequency (RF) Modem User Guide
21
There must be an active DTR signal to automatically detect an RS-232 serial connection. If the serial cable or end
device does not include an active DTR signal, disable IP socket mode (
ES = 0
) using XCTU, the web configuration, or
Device Cloud.
By default, RS-485 mode is disabled (
4E
= 0) and IP socket mode is enabled (
ES
= 1). So, by default, RS-232 mode is
selected if DTR is present. Otherwise, IP socket mode is selected. Use the
4E
and
ES
configuration parameters to
select other modes, independent of DTR, which may not be present on a serial port connection.
USB mode
The mini USB port is used for configuration and basic serial communication. To use the mini USB port, install the XLR
PRO USB driver (Windows only) on the host PC. (The driver is available at
productdetail?pid=5603&type=drivers
.) When connected via the mini USB port, the XLR PRO appears as a virtual COM
port on the host. XLR PRO detects an active virtual DTR signal to determine if a USB connection is active.
When communicating to the XLR PRO using the USB mode, serial settings and flow control are not used. Serial
settings (baud rate, parity, and stop bits) can be set to any value on the host PC and do not affect the XLR PRO
connection. If a host application requires flow control, use RS-232 serial mode.
Serial mode
When serial mode is the primary interface, the Serial Data In (green) LED lights for about three seconds. Serial mode
can be either RS-232 or RS-485/422, depending on serial mode selection. The following parameters must be
configured to match the host device, regardless of whether RS-232 or RS-485 is selected:
•
BD:
Baud rate (See the AT command table for limits)
•
NB:
Parity (None, Even, or Odd)
•
SB:
Stop bits (1 or 2)
RS-232
RS-232 connections support hardware flow control using CTS and RTS and require matching parameters on the XLR
PRO and the host device. This includes the following:
•
D6
: RTS flow control. If enabled, then XLR PRO will not output data unless RTS is asserted. The host device should
not de-assert RTS for long periods of time to avoid filling the serial transmit buffer. If an RF data packet is received,
and the serial transmit buffer does not have enough space for all of the data bytes, the entire RF data packet will
be discarded.
•
D7
: CTS flow control. If enabled, then XLR PRO will not assert CTS low unless it can handle more data from the
host.
•
FT
: Flow control threshold. If CTS flow control is enabled (with D7 parameter), the XLR PRO deasserts CTS when
the serial receive buffer reaches the threshold defined by the FT parameter. Once CTS is de-asserted, it will not be
asserted again until the receive buffer has 17 bytes less than the threshold defined by FT. By default, FT is 65 bytes
less than the maximum space available for receive data.
RS-485/422
An RS-485 connection requires that 4E=1 and it also requires matching parameters on the XLR PRO and the host
device. This includes the following:
•
4E
: Enable RS-485/422. If 4E is set to 0, then the XLR PRO will use RS-232. This parameter needs to be set to 1 in
order to use RS-485/422 on the serial port.
•
4D
: Full duplex (4-wire) or half duplex (2-wire) operation. A default value of 0 selects half duplex operation and 1
selects full duplex.