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• x0B Vertical Tab

• x08 Backslash

The change to the method used to represent special characters has been made to allow for all ASCII char-
acters to be used, and to allow for hexadecimal data to be captured.

Note In ﬁrmware revisions 2 and lower, special characters are speciﬁed as escape characters. In revisions
2 and above, special characters are represented by their ASCII representations in hexadecimal.

In some serial protocols, the start of a packet is speciﬁed by a preceeding period of inactivity on the serial
bus. The Idle Time Before Start parameter can be used to specify an idle time, which is exceeded will
trigger the serial port to start capturing serial data.

Note If the serial port is capturing data and a subsequent idle time occurs, the capture process will restart
and captured data will be discarded.

A serial capture stop string of up to 10 characters can also be provided. Again using the NMEA example,
all NMEA messages end with a carriage return and line feed and so the serial capture stop strings in each
case will be the same and will be “\r\n” or \x0D\x0A in revision 2 and above ﬁrmware. In most
instances, the serial stop strings will be the same for all messages.

Note If a start string is speciﬁed without a stop string, or the stop string is never encountered, the serial port
will capture characters until the max-time or max-chars is reached, the next measurement interval occurs or
256 characters are received.

An optional serial request string can be sent, on each measurement interval, to an external device. The
purpose of the request sting is to request data from an external sensor or system. The request string can be a
maximum of 10 characters and can be entered as text. Special characters like carriage return and line feed
can be inserted using escape sequences or their ASCII representations as described earlier in the chapter.

The ORB implements the MODBUS communications protocol standard as a master, which enables
communication with many slave devices connected to the network. The ORB can be conﬁgured to peri-
odically request speciﬁc data from slave MODBUS devices on the network and transmit that data at speci-
ﬁed intervals.

Up to ten MODBUS data requests can be conﬁgured on the ORB; these data requests can either be from
ten individual slave devices or multiple requests from the same device.  For each of the ten data reads, the
slave  address,  function  and  register  address  need  to  be  speciﬁed.    The  slave  address  will  be  speciﬁed  by  the
manufacturer of the device that is attached to the ORB; in some cases, slave devices allow their addresses
to  be  conﬁgured.    The  function  speciﬁes  the  type  of  data  to  be  read  from  the  slave  device.    The  ORB
supports the following types of data reads:

• Disabled - the paricular MODBUS channel is not used

• Read Coil - a 1 bit data value

• Read Discrete - a 1 bit data value

• Read Holding - a single 16 bit holding register

• Read Input - a 16 bit input register

• Read Holding (32 bits, Little Endian register order) - a 32 bit holding register

• Read Holding (32 bits, Big Endian register order) - a 32 bit holding register

• Read Input (32 bits, Little Endian register order) - a 32 bit input register

ORB User Guide, Release 1.1

6.2. Serial Interface