300-R010-45G datasheet(29/36 Pages) MAGNETROL

29 / 36 page

MEMORY MAP

Modbus sets up the data in a memory map. The memory

map is set up in registers that are 2 bytes in length. The read

only registers are numbered form 30001 to 39999. The

read/write registers are numbered from 40001 to 49999. In

order to access these registers; an offset is sent. For exam-

ple, if the data in register 30001 is to be read, an offset of

0000 is sent.

Individual bits in the bit registers are addressed by a sepa-

rated map. The read only bits are numbered from 10000 to

19999 and the read/write bits are numbered from 0 to 9999.

In the XXXX unit, both addresses will access the same bit.

The offset for these bits is the same as the registers. For

example, if 10003 is to be read, and offset of 0002 is sent.

MODEL 300/301 MODBUS MAPPING

A maximum and minimum value of 0 indicates that the value

is Read Only. Care must be taken when disabling relays. The

relay will hold the last state when it is disabled. RS-485 is

used for external communications using Modbus.

The Model 300/301 Transmitter uses the Modbus RTU pro-

tocol. The user must enter the BAUD rate and the parity that

the master will be using. See page 24 for configuration

instructions. Each of these parameters must be set at the

unit before communication can occur.

1. BAUD rate: 1200, 2400, 4800, 9600.

2. Parity: Odd (8, O, 1), Even (8, E, 1), or None (8, N, 2).

PROGRAMMING cont.

CHARACTER FRAMING

The Model 300/301 is factory configured for 9600 baud,

even parity, and 1 stop bit. In serial communication, the bits

are sent out one at a time, least significant bit first. These are

surrounded by a start bit (always low) and a parity bit or a

stop bit (if a parity bit, it will be followed by a stop bit)

(always high).

Figure 19

MESSAGE FRAMING

All messages start and end with an idle time of 3.5 character

times. For the 300/301 this value is approximately 4 ms at

9600 baud. This will let all the units know that the next byte

to follow is the address field.

Figure 20

Because of this method for determining the address byte,

the entire message must be sent in a continuous stream. If

an idle time of more than 1.5 character times occurs before

the completion of the message, the next byte received will

be assumed an address byte and the previously received

bytes will be ignored.

Start

Stop

Address

Function

Data

CRC Check

3.5 Character

Times

3.5 Character

Times

11 Bit Times

Less than 1.5

Character Times

Stop

Parity

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