File Transfers; Obtaining Relay Files Using Modbus - GE B30 Communications Manual

CHAPTER 2: MODBUS COMMUNICATION
Table 2-10: Master and slave device packet transmission example
Master transmission
Packet format
SLAVE ADDRESS
FUNCTION CODE
CRC - low order byte
CRC - high order byte

2.3 File transfers

2.3.1 Obtaining relay files using Modbus

2.3.1.1 Description
The UR has a generic file transfer facility, meaning that you use the same method to obtain all of the different types of files
from the unit. The Modbus registers that implement file transfer are found in the "Modbus File Transfer (Read/Write)" and
"Modbus File Transfer (Read Only)" modules, starting at address 3100h in the Modbus Memory Map. To read a file from the
UR, use the following steps:
1. Write the filename to the "Name of file to read" register using a write multiple registers command. If the name is
shorter than 80 characters, you may write only enough registers to include all the text of the filename. Filenames are
not case sensitive.
2. Repeatedly read all the registers in "Modbus File Transfer (Read Only)" using a read multiple registers command. It is
not necessary to read the entire data block, since the UR remembers which was the last register you read. The
"position" register is initially zero and thereafter indicates how many bytes (2 times the number of registers) you have
read so far. The "size of..." register indicates the number of bytes of data remaining to read, to a maximum of 244.
3. Keep reading until the "size of..." register is smaller than the number of bytes you are transferring. This condition
indicates end of file. Discard any bytes you have read beyond the indicated block size.
4. If you need to re-try a block, read only the "size of.." and "block of data", without reading the position. The file pointer is
only incremented when you read the position register, so the same data block is returned as was read in the previous
operation. On the next read, check to see if the position is where you expect it to be, and discard the previous block if it
is not (this condition would indicate that the UR did not process your original read request).
The UR retains connection-specific file transfer information, so files may be read simultaneously on multiple Modbus
connections.
2.3.1.2 Other protocols
All the files available using Modbus can also be retrieved using the standard file transfer mechanisms in other protocols
(for example, TFTP or Manufacturing Message Specification, MMS).
2.3.1.3 COMTRADE, oscillography, data logger, and PMU record files
Oscillography, data logger, and PMU record files are formatted using the COMTRADE file format per IEEE C37.111 (1999 or
2013) Standard Common Format for Transient Data Exchange (COMTRADE) for Power Systems. The files can be obtained in
either text or binary COMTRADE format.
The EnerVista UR Setup software includes the ability to work with COMTRADE files. Access File > COMTRADE Utility. See
the Waveforms chapter of the EnerVista Viewpoint Monitoring Instruction Manual (accessible on the website) for
information on how to use the tool.
UR FAMILY – COMMUNICATIONS GUIDE
Slave response
Example (Hex) Packet format
11 SLAVE ADDRESS
39 FUNCTION CODE
CD ERROR CODE
F2 CRC - low order byte
CRC - high order byte
FILE TRANSFERS
Example (Hex)
11
B9
01
93
95
2-7
2