File Access Block

With this block you can save data from your robot in files on your NXT. After writing data to a file, you must use another File Access block to close the file before you can read or delete the file using a third File Access block.

For example, to write to a file and then read from the same file, you must close the file between those two actions. You would need three File Access blocks to accomplish this task: the first File Access block (with "Write" selected in its configuration panel) would write data to a file; a second File Access block positioned somewhere later in the program would have to be set to close the same file; a third File Access block (with "Read" selected in its configuration panel) would be able to read the file. These three blocks could be positioned right next to each other or could be spaced throughout your program.

Writing to an existing file will add data to the end of the file; it will not erase any pre-existing data. To re-write a file, first use a File Access block that deletes the file. Then use another File Access block to write to a new file of the same name.

1. This icon indicates whether the block is set to Write, Read, Close, or Delete a file.

Configuring the File Access Block

1. Use the pull-down menu to specify whether you want to Write, Read, Close or Delete a file.
2. Use the input box to either name a file (if you are writing to it for the first time) or specify an existing file by typing it in the input field or by selecting it in the pull-down menu.
3. Choose whether the file should be a text or number file.

Configuring the File Access block’s Data Hub

You can control the File Access block dynamically by connecting data wires (from other blocks’ data hubs) to the File Access block’s data hub.

Open a block’s data hub by clicking the tab at the lower left edge of the block after it has been placed on the work area.

Data wires carrying input information to a block are connected to the plugs on the left side of its data hub. Data wires carrying output information are connected to the plugs on the right side.

[A] Input plug
[B] Output plug
[C] Number data wire (yellow)
[D] Logic data wire (green)
[E] Text data wire (orange)
[F] Broken data wire (gray)

Passing data from the input plug to the output plug

If an input plug has a corresponding output plug (see A above), the input data will pass through from the input plug to the output plug without being changed. In this case, you can only use the output plug if the input plug is connected to an input data wire; connecting an output data wire to such an output plug without a connected input data wire will cause the output data wire to be "broken" (and colored gray).

Data wires carry specific types of data

Each data wire carries a specific type of data between blocks. For example, if a data wire is dragged from a logic plug on a block’s data hub, it can only be connected to a logic plug on another block’s data hub. The chart below shows what kind of data each plug can accept or send out.

Data wire colors

Data wires are identified with specific colors: wires carrying number data are colored yellow, wires carrying logic data are colored green, and wires carrying text data are colored orange.

"Broken" data wires

If you try to connect a data wire to a plug of the wrong data type, the data wire will be broken (and colored gray). You will not be able to download your program if a data wire is broken.

If you click a broken wire you can read why it is broken in the small help window in the lower right corner of the work area.

Data must be within the possible range of the plug

If an input data wire transmits a value outside the possible range of the plug it is connected to, the block will either ignore the value or change it to a value within its range. For plugs that allow just a few input values (example: just 0, 1, or 2), the plug will ignore the input if a value arrives outside its range.

For plugs that accept larger input ranges (example: 0 – 100), the plug will force any input outside its range to fit. For example, if a Move block’s Power plug receives an input value of 150, the block will change the input value to 100 (i.e., a number within the Power plug’s range).

This chart shows the different characteristics of the plugs on the File Access block’s data hub:

	Plug	Data Type	Possible Range	What the Values Mean	This Plug is Ignored When...
	Filename	Text	15 character maximum	Filename
	Initial File Size	Number	0 - 32767	Valid only when file is first created (i.e., "Write" and file doesn't currently exist). Determines file size. Can be used to avoid time penalty associated with auto-resizing a file.	Action not Write, or file already exists
	Text	Text		Text to write	Action not Write
	Number	Number	-2147483648 - 2147483647	Number to write	Action not Write
	Error	Logic	True/False	True if an error occurred in the block (Writing and file is full, Reading and at end of file, Deleting and file didn't exist)
	Text out	Text		Text that was read	Action not Read
	Number out	Number	-2147483648 - 2147483647	Number that was read	Action not Read