MATLAB Function Reference

fwrite (serial) - Write binary data to device

Syntax

fwrite(obj,A) fwrite(obj,A,'precision') fwrite(obj,A,'mode') fwrite(obj,A,'precision','mode')

Arguments

`obj`	A serial port object.
`A`	The binary data written to the device.
`'``precision``'`	The number of bits written for each value, and the interpretation of the bits as character, integer, or floating-point values.
`'``mode``'`	Specifies whether data is written synchronously or asynchronously.

Description

fwrite(obj,A) writes the binary data A to the device connected to obj.

fwrite(obj,A,'precision') writes binary data with precision specified by precision.

precision controls the number of bits written for each value and the interpretation of those bits as integer, floating-point, or character values. If precision is not specified, uchar (an 8-bit unsigned character) is used. The supported values for precision are listed below in Remarks.

fwrite(obj,A,'mode') writes binary data with command line access specified by mode. If mode is sync, A is written synchronously and the command line is blocked. If mode is async, A is written asynchronously and the command line is not blocked. If mode is not specified, the write operation is synchronous.

fwrite(obj,A,'precision','mode') writes binary data with precision specified by precision and command line access specified by mode.

Remarks

Before you can write data to the device, it must be connected to obj with the fopen function. A connected serial port object has a Status property value of open. An error is returned if you attempt to perform a write operation while obj is not connected to the device.

The ValuesSent property value is increased by the number of values written each time fwrite is issued.

An error occurs if the output buffer cannot hold all the data to be written. You can specify the size of the output buffer with the OutputBufferSize property.

If you use the help command to display help for fwrite, then you need to supply the pathname shown below.

help serial/fwrite

Synchronous Versus Asynchronous Write Operations

By default, data is written to the device synchronously and the command line is blocked until the operation completes. You can perform an asynchronous write by configuring the mode input argument to be async. For asynchronous writes:

The BytesToOutput property value is continuously updated to reflect the number of bytes in the output buffer.
The M-file callback function specified for the OutputEmptyFcn property is executed when the output buffer is empty.

You can determine whether an asynchronous write operation is in progress with the TransferStatus property.

Synchronous and asynchronous write operations are discussed in more detail in Writing Data.

Rules for Completing a Write Operation with fwrite

A binary write operation using fwrite completes when:

The specified data is written.
The time specified by the Timeout property passes.

Supported Precisions

The supported values for precision are listed below.

Data Type	Precision	Interpretation
Character	`uchar`	8-bit unsigned character
	`schar`	8-bit signed character
	`char`	8-bit signed or unsigned character
Integer	`int8`	8-bit integer
	`int16`	16-bit integer
	`int32`	32-bit integer
	`uint8`	8-bit unsigned integer
	`uint16`	16-bit unsigned integer
	`uint32`	32-bit unsigned integer
	`short`	16-bit integer
	`int`	32-bit integer
	`long`	32- or 64-bit integer
	`ushort`	16-bit unsigned integer
	`uint`	32-bit unsigned integer
	`ulong`	32- or 64-bit unsigned integer
Floating-point	`single`	32-bit floating point
	`float32`	32-bit floating point
	`float`	32-bit floating point
	`double`	64-bit floating point
	`float64`	64-bit floating point