SD File Functions

You can use Windows Explorer to store any type of file onto an SD card, such as .html or .jpg. The SD File Functions enable your Ladder application to read and write these files in 'chunks' of 512 bytes.

Note ♦

These functions can only run on files that observe the 8.3 naming convention; the file name cannot exceed 8 characters, and the file extension cannot exceed three.

Using SD File Functions

Each read or write operation requires three functions: Open File, Read or Write, and Close File. The functions are located on SD>SD File Utilities.

Open SD File
Note that there are separate Open File functions for both Read and Write. Open File must be used to activate the correct file in the correct folder before running a read or write function.
Read Next Chunk
Reads a specified file from a specified folder to an operand vector in 'chunks' that are 512 bytes long.
Write Next Chunk
Writes data chunks 512 bytes from an operand vector to a specified file on the SD card.
Close File.
There are separate Close File functions for both Read and Write.

The examples below show the functions and the System operands required to run read and write operations.

Read File: Example

Note the use of SBs 324, 325, and 326. These enable the Read Next Chunk function to continue reading data chunks until it has completed reading the entire file.

Write File: Example

Functions

Read From SD File: Open

Parameter	Purpose
Select Folder	Select the folder, or use an operand to assign a number at run time using the following values: Alarms: 0 ♦ DT main folder: 1 ♦ DT1–4: 101 to 103 ♦ Log: 3 ♦ System: 4 ♦ User_app: 5 ♦ Trends main folder - 600 ♦ Trends1-4: 600 to 603 ♦ SdBLocks: 9 ♦ Excel main folder: 100 ♦ Excel1-4: 1000 to 1003 ♦ Web: 11
File name	Either enter the file name, or provide it via operand.
File size	When the function runs, this reports the size of the file, in bytes.

Read File: Get Next Chunk

Parameter	Purpose
Read: File Chunk Buffer	This the start of the vector that holds the data read from the file. This vector is 512 bytes long.
Read: File Chunk Length	This shows the length of the chunk that is currently read. Note that the final chunk, containing the last of the file data, will generally be LESS than 512 bytes.

Read File: Close

Run this when entire files has been read.

Write From SD File: Open

Parameter	Purpose
Select Folder	Select the folder, or use an operand to assign a number at run time using the following values: Alarms: 0 ♦ DT main folder: 1 ♦ DT1–4: 101 to 103 ♦ Log: 3 ♦ System: 4 ♦ User_app: 5 ♦ Trends main folder - 600 ♦ Trends1-4: 600 to 603 ♦ SdBLocks: 9 ♦ Excel main folder: 100 ♦ Excel1-4: 1000 to 1003 ♦ Web: 11
File name	Either enter the file name, or provide it via operand. Note that: -If the file does not exist on the SD -and the SD card is Write-enabled the function will create the file.
File size	When the function runs, this reports the size of the file, in bytes.

Write File: Get Next Chunk

Parameter	Purpose
Write: File Chunk Buffer	This the start of the vector that holds the data that will be written to the file. The function takes 512 bytes of data.
Write: File Chunk Length	Enter the number of bytes to be written to the SD file.

Write File: Close

Run this when entire files has been written.

Delete File

Use this to delete any file on the SD card

Note ♦	These functions can only run on files that observe the 8.3 naming convention; the file name cannot exceed 8 characters, and the file extension cannot exceed three.
♦	Use SB 358, Delete File in Progress, as a condition to running the function

Parameter	Purpose
Select Folder	Select the folder, or use an operand to assign a number at run time using the following values: Alarms: 0 ♦ DT main folder: 1 ♦ DT1–4: 101 to 103 ♦ Log: 3 ♦ System: 4 ♦ User_app: 5 ♦ Trends main folder - 600 ♦ Trends1-4: 600 to 603 ♦ SdBLocks: 9 ♦ Excel main folder: 100 ♦ Excel1-4: 1000 to 1003 ♦ Web: 11
File name	Either enter the file name, or provide it via operand.
Status Messages	This MI is a bitmap; a bit turns ON to indicate status. The MI is initialized when the function starts. All bits OFF – No errors, and the SD card is idle Bit 1 – SD Card internal error. Bit 2 – Delete Failed Bit 3 - No SD card found, or the card is locked (Write-enable OFF) Bit 5– Path not found Bit 7 - The SD card has failed (Check SI 66)
Success Bit	Turns ON when the file is deleted. It remains ON until it is reset by the application,.

SD File Information

Use this function to check if a specific file is located in a specific SD folder, and get specific file details.