8
Chapter 3 - Definitions
DD:
Device Description files
are necessary to configure your FF-BUS host software. The
DD files explain the specific configuration and features to your host network so it understands
how to use the device.
Resource Block (RS):
This function block contains basic information about the FF-BUS
interface.
Transducer Block (TB):
This block makes the connection to the meter and presents the
process variables to the lower blocks. Most of the configuration setup is done in this block.
AI (Analog Input) Block:
Although this is actually digital process data coming from the
instrument (output), it is still referred to as an AI Block. This FF-BUS interface has four
analog input blocks: AI1, AI2, AI3, and AI4.
AO (Analog Output) Block:
Although this is a digital command being sent to the instrument
(input), it is still referred to as an AO Block. The 600/700 Series FF-BUS interface has one,
labeled AO.
Modbus:
Modbus is another digital communication protocol and is only relevant here
because the Sierra FF-BUS interface uses Modbus as an intermediary between the meter and
the FF-BUS interface. For special configuration, the user will only need a rudimentary
knowledge of Modbus.
MODBUS_REG_SETUP_1 to 4
: This is where AI1,2,3,4 and AO are configured as
PV1,2,3,4, and Final Value. These are 32 bit registers the can configured multiple data types
in various Byte order.
MODBUS_REGS_1 to 4:
There are four groups of ten Modbus R/W registers that can be
used for static variables such as serial number, calibration date, total reset, and meter full
scale. These only have limited use, and may not be able to be seen with all FF-BUS devices.
32 bit float:
Also known as Real or IEEE-754 single precision. The 32 bit float is a common
data encoding scheme that provides 1 bit for the sign, 8 bits for an exponent, and 23 bits of
significant numbers. In Modbus the Byte order is normally 1-0,3-2, however FF-BUS
interface allows it to be changed if needed.
16 bit short integer:
This is a 16 bit number ranging from 0-65,535 (2
16
). The Byte order is
0,1.
32 bit long integer:
This combines two 16 bit Modbus registers to make a number as high as
4,294,967,296 (2
32
). The Byte order is 1-0,3-2. The FF-BUS will see this as one 32 bit
integer.
String (Character):
A 16 bit Modbus register would contain 2 ASCII characters (8 bits each)
in 0-1 Byte order. So ox 41 42 would equal “A B”.