CAS CI-400 Series, Руководство пользователя

Страница: 108 / 120

109
Appendix 6>MODBUS-RTU PROTOCOL
The registry read and write shown below of MODBUS-RTU protocol can be managed
based on the requirements included in the reference document regarding the
Modicon
PI-MBUS-300 standard.
For selection of communication with Modbus-RTU, the serial communication settings
paragraph has been included.
If specific data has been recorded directly in EEPROM type memory, it is
recommended that unnecessary work at the aforementioned position be avoided as the
memory is limited in its write activation (100,000).
The below number is, when coming after 0x, is described in a decimal or a
hexadecimal method.
MODBUS-RTU DATA FORMAT
Data transferred by the Modbus-RTU protocol has the following characteristics.
- Start bit 1
- Data bit 8 (smallest bit sent first)
- Parity bit setting (instrument setting)
- Stop bit setting (instrument setting)
MODBUS SUPPORTED FUNCTIONS
From the commands capable of being used in the Modbus-RTU protocol, only the following
are used in communication management with the instrument. Other commands may not be
accurately interpreted and may cause error or shutdown the system.
Function Explanation
03(0x03) READ HOLDING REGISTER
16(0x10)
PRESET MULTIPLE REGISTERS
The request cycle is integrated with the preset communication speed. (The instrument requires
a transfer delay of at least 3 bytes to reply to the request)
Delay parameters exist in the serial communication setting, and directly affect the number of
request possible in a unit time by additionally delaying the reply from the instrument.
For additional information about this protocol, refer to the PI_MBUS_300 normal technical
specifications.
Typically, the request and reply for the slave instrument is composed as follows.