Varec Network Adapter 4000, Installation And Operation Manual, Page: 52 / 80

Theory of Operation Tank Gauge Transmitter
42 Installation and Operations Manual
The supported Modbus functions and exceptions are indicated in the following tables.
Table 7-1: Modbus Functions
Table 7-2: Modbus Exception Responses
7.10 Mark/Space Host Interface
The Mark/Space interface provides compatibility with existing Mark/Space data
highways. The interface operates in one of two modes.
•
Transmitter Emulation Mode
•
Varec 1800 Transmitter Emulation
•
Varec 1900 Transmitter Emulation
•
Mark/Space Modbus Communication Mode
When operating in the 1800 or 1900 emulation mode, the ATT is compatible with all
existing Varec field interfaces such as the Tank Polling Unit (TSU) or RTU 8130.
The ATT automatically determines if it is being polled as an 1800/1900 transmitter.
When polled, the ATT will respond based on the configured emulation mode. The ATT
can be configured to support the following encoding formats:
•
Imperial Fractional
•
Imperial Decimal
•
Metric, 0-20 meter
•
Metric, 0-30 meter
Function Number Function
01 Read Digital Outputs
02 Read Digital Inputs
03 Read Analog Output Registers
04 Read Analog Input Registers
05 Write Single Digital Output
06 Write Single Analog Output Register
08 Loopback Test
15 Write Multiple Digital Outputs
16 Write Multiple Analog Output Registers
65 Read Floating Point Registers
66 Write Floating Point Registers
Number Exception
01 Illegal Function
02 Illegal Address
03 Illegal Data
04 Busy