Name: Satec PM130EH SERIES
Brand: Satec
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2 MODBUS FRAMING

2.1 Transmission Mode

The protocol uses the Modbus Remote Terminal Unit (RTU) transmission mode. In RTU mode, data is

sent in 8-bit binary characters. The 8 bit even parity or 8 bit no parity data format must be selected when

configuring the instrument communications. The data format is shown in the following table.

Table 2-1 RTU Data Format

Field No. of bits

Start bit 1

Data bits c 8

Parity (optional) 1

Stop bit 1

c Least significant bit first

2.2 The RTU Frame Format

Frame synchronization is maintained in RTU transmission mode by simulating a synchronization message.

The receiving device monitors the elapsed time between receptions of characters. If three and one-half

character times elapse without a new character or completion of the frame, then the device flushes the

frame and assumes that the next byte received will be an address. The frame format is defined below.

The maximum query and response message length is 256 bytes including check characters.

RTU Message Frame Format

T1 T2 T3 Address Function Data CRC Check T1 T2 T3

8 bits 8 bits N * 8 bits 16 bits

2.3 Address Field

The address field contains a user assigned address (1-247) of the instrument that is to receive a message.

Address 0 is used in broadcast mode to transmit to all instruments (broadcast mode is available only for

functions 06 and 16). In this case all instruments receive the message and take action on the request, but

do not issue a response. In the PM130EH, the broadcast mode is supported only for register addresses

287-294 and 301-302 (reset energies and maximum demands), 3404-3415 (reset/clear registers), and

4352-4358 (real-time clock registers).

2.4 Function Field

The function field contains a function code that tells the instrument what action to perform. Function codes

used in the protocol are shown below in Table 2-2.

Table 2-2 Modbus Function Codes

Code (decimal) Meaning in Modbus Action

03 Read holding registers Read multiple registers

04 Read input registers Read multiple registers

06 Preset single register Write single register

16 Preset multiple registers Write multiple registers

08 Loop-back test Communications test

NOTE Broadcast mode available only for functions code 06 and 16.

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Satec PM130EH SERIES Specifications

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