Lenze E94P PositionServo Modbus - Manual (Page 26)

26 P94MOD01C
Protocol Implementation
5.4 Endian Format
Modbus uses “big-endian” representation of the register data. This means that when a numerical value that is
larger than a single byte is transmitted, the MOST significant byte (MSB) is sent first, e.g.
• 16-bit integer value 0x1234 = 2 bytes of 0x12 and 0x34
• 32-bit integer value 0x12345678 = 4 bytes of 0x12, 0x34, 0x56 and 0x78
5.5 Registers Access
• Care should be taken when accessing registers from multiple sources such as multiple clients or the drive
Indexer program as data could be over written or out of sequence
• Writing to the EPM area of memory simultaneously writes to the RAM area too
• Writing to the EPM area of memory should be done conservatively as the EEPROM (EPM) has a typical life
expectancy of 1 million writes
5.5.1 Register Reading
Use the function code “03 (0x03) Read 4X Holding Registers” to read an adjoining block of holding registers in
a remote device.
NOTE:
Do NOT attempt to read any write-only variables. Attempting to read a write-only variable can result
in erroneous data.
5.5.2 Register Writing
No discrete coil access (function code 1) is provided for PositionServo Drive. Use the “16 (0x10) Write Multiple
Registers” function to write binary values. This requires the user programming to pack bits into user registers.
The function code “16 (0x10) Write Multiple Registers” is used to write a block of adjoining registers (1-123,
Master device dependent) in a remote device.
NOTE:
Do NOT attempt to write to any read-only variables. Attempting to write to a read-only variable can
result in drive fault (F41).
5.6 No Response Conditions
The PositionServo Drive will not respond to any message that:
•
contains one or more parity errors
• has an invalid CRC value
• was not directed to the drive’s network address
• is not at least 8 bytes long (minimum required for the supported functions)
• is more than 18 bytes long (maximum allowed before input buffer overflow occurs)