Robot App Store Developer Program


Knowledge Base

Lego NXT File Handling- Introduction

  By Anna Sandler

This is an advanced topic, please familiarize yourself with "What is a NXT Bluetooth Telegram" tutorial before you continue reading this chapter.

Files handling command types

Files handling commands are part of the "System commands".
There are two relevant command types for a system command:
  • 0x01 for a command with reply message, and
  • 0x81 for a command without the reply message.

Some of the file handling commands require a reply message such as open file commands or a read command.

File names

File name format consists from:
[name, up to 15 ASCII characters].[type, 3 ASCII characters][string null terminator 0x00].
The system is case insensitive, meaning uppercase characters are treated the same as lower case characters.

File types

The following file types are supported:
  • RXE: NXT’s executable files, compiled from NXT-G, LabVIEW, or another compatible programming environment.
  • RPG: 5-step programs created using the “NXT Program” user interface on the NXT brick.
  • RTM: Built-in “Try Me” programs.
  • RIC: Image files for use with the NXTDrawPicture syscall method in .RXE programs.
  • RSO: Sound files.
  • SYS: Internal NXT firmware files.
  • CAL: Sensor calibration file.
  • TXT: ASCII text file using carriage return/line feed (CR/LF, Windows) end-of-line convention.
  • LOG: Also an ASCII text file, created by the NXT data logging functionality.

File handling workflow

On the NXT brick’s flash memory, files are organized in a simple, flat, file-system without folders.

File should be opened first before read or write.
The return message of the opening commands includes the handler id of the opened file.
The system registers each handler ids and its file name that is currently opened in an internal table.
Retrieving an opened handler id is always possible using the ResolveHandle command that gets the file name and retrieved open file handler id (will be discussed in later posts).

Open handlers must be closed when are no longer in use.
All open handlers are closed automatically at the end of the program execution.
When the file is closed automatically, unused space inside the specified file is removed, in order to maximize the free space on the device.


  • 16 open handlers (read and write) for each thread;
  • 4 open handlers for writing purposes at the same time;
  • 127 maximum files can be created in the system. (If there is enough free space.)
  • A delay of 6 milliseconds must be passed between the file handling command and any other command.
  • File name is allowed to be up to 15 characters, plus 3 characters for the file type and a NULL terminator ('\0')
  • Telegram length is limited to 64 bytes.

File handling errors

File handling commands return a descriptive error reason for failure at the reply message (if requested).
Open file commands will retrieve a fake handler id in case of failure.
The error code can be found in the status byte of each response command.

The following is a list of file handling errors:
  • 0x00- Success - the command that has requested this response has been successfully executed.
  • 0x81- No more handlers. The system is not able to allocate any more file handlers for this thread. One of the reasons for this error can be a maximum limit of 16 opened file handlers that has already been reached for this thread. Try to send CloseFile command to one of the open file handlers that is no longer in use, then resend the open file command again.
  • 0x82- No space
  • 0x83- No more files. The system is not able to create any more files. Most likely, the reason is that you’ve reached the limitation of 127 files the can be saved on the NXT brick’s flash memory. Try deleting files that are not in use and resend the create file command again.
  • 0x84- End of file expected. Write request exceeded the space available for the file. Partial write performed. One of the reasons can be a wrong file size calculation when it was created due to missing null terminator bytes after the file name in case the name is shorter than 15 characters.
  • 0x85- End of file. File operation reached the end of the file.
  • 0x86- Not a linear file.
  • 0x87- Specified file not found.
  • 0x88- Handler already closed.
  • 0x89- No linear space. The system is not able to allocate requested linear file system space for specific file.
  • 0x8A- Undefined error.
  • 0x8B- File is busy. The system cannot acquire file handler for specified file because some other operation has opened the file.
  • 0x8C- No write buffers. The system cannot open the file for write operation because all write buffers are already in use. There is a limitation of 4 files that can be opened for writing at the same time. Try to close one of the opened files that are no longer is use and resend the open file for write command.
  • 0x8D- Append is impossible. Not a textual file or the file is already full.
    The only way to use FileOpenAppend command successfully, is to create a textual file, leave some empty space and close it using the FileClose command.
    Bear in mind that once the file is automatically closed by the file system, all the free space in the file is removed to optimize total free space in the brick.
  • 0x8E- File is full. The allocated space for specified file is full. No more write operations allowed.
  • 0x8F- File name exists. The system has failed to create or rename the file due to name collision. Try to resend the command with different name.
  • 0x92- Illegal file name. The file name that has been provided is illegal. Make sure that the correct file name format is used: [15].[3] characters.
    File type can be only one of the types that has been described in the file types section above.
  • 0x93- Illegal handler. the allocated space for specified file is full, or the file has been opened for other purposes.

What's next?

Let's move forward and learn how to create a file on NXT's file system over Bluetooth communication protocol (LCP)

read here why do men have affairs why men cheat on beautiful women
my wife cheated now what read looking for affair
signs of a cheater what makes married men cheat married men that cheat
all about abortion ru486 abortion pill cost misoprostol and abortion
abortion cost without insurance site post abortion
canada drug pharmacy coupon internet drug coupons

Related Robot-Apps™