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10.3.3 Slave Addresses and Sending Requests

Each slave device on the communication bus has its own dedicated address and responds only

to addresses addressed by the master. The packet returned to the master has the same address in

the slave address field as the request packet. These addresses are programmable and range from

0 to 255.

Slave address 0 is a transfer command that allows the master to send the same packet to all

devices at once. All slaves follow the packet's instructions but do not respond. The transfer request

is only useful for functions 6 and 10, which represent the presetting of a single register and

the presetting of multiple registers, respectively. See Tables 1.3 and 1.4.

10.4 function number

The function number of a packet tells the addressed slave what action to perform. Nexus supports

the following Modus feature numbers.

Table 1.1 function number

function number

hexadecimal

decimal system

03H

3

06H

6

10H

16

Desc

read hold register

Preset a single register

Preset multiple registers

10.4.1 Function No. 03: read hold register

This feature allows the master to read one or more parameter values (data registers) from a

Nexus slave. This data register is a 16-bit value that is transmitted in the "Big Endian" format.

The high byte is read first and the low byte is read later.

BIG-ENDIAN means that the low order bytes are arranged at the low end of memory and

the high order bytes are arranged at the high end of memory

The master sends a packet defining a start register and the number of registers to read for

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