Composition Of Message - Teledyne 7500 Instruction Manual

Teledyne Analytical Instruments
5.2

Composition of message

Command message and response message consist of 4 fields ; Station No., Function code,
Data and Error check code. And these are sent in this order.
Station No. (1 byte)
Function code (1 byte)
Data (2 to 133 bytes)
Error check code (CRC-16) (2 bytes)
Fig. 5.1 Composition of message
In the following, each field is explained.
(1) Station No.
Station No. is the number specifying a slave station. Only a slave station that corresponds to
a value to which "Station No." is set on the analyzer maintenance mode display executes a
command.
(2) Function code
This is a code to designate the function executed at a slave station. For details, refer to
section 5.4.
(3) Data
Data are the data required for executing function codes. The composition of data varies with
function codes. For details, refer to chapter 6.
A register number is assigned to each data in the analyzer. For reading/writing the data by
communication, designate the register number.
Note that the register number transmitted on message is expressed as its relative address.
The relative address is calculated by the following expression.
* * Relative address * * (The lower 4 digits of the Register number) - 1
For example, when the resister number designated by a function code is 40003,
* * Relative address = (The lower 4 digits of 40003) - 1
= 0002
is used on the message
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