2.2 - Single Value Functions
Published on LabJack (https://labjack.com)

Home > Support > Software & Driver > API Documentation > LJM User's Guide > 2 - Function Reference > 2.2 - Single Value Functions

2.2 - Single Value Functions

Summary

To access device data one value at a time, use the following functions. See the Modbus map to see what values can be accessed. 

Name Functions

Name functions access data by a name, such as "AIN5" for analog input 5.  

Address Functions

Address functions access data by an address and data type. For example, analog input 5 ("AIN5") would have address 10 and a 32-bit floating point type.


Need to read or write multiple values at once? Use the Multiple Value Functions.

2.2.1 - eWriteName

Write one value, specified by name.

Syntax

LJM_ERROR_RETURN LJM_eWriteName(
                      int Handle, 
                      const char * Name, 
                      double Value)

Parameters

Handle [in]
A device handle. The handle is a connection ID for an active device. Generate a handle with LJM_Open or LJM_OpenS.
Name [in]
The name that specifies the Modbus register(s) to write.  Names can be found throughout the device datasheet or in the Modbus Map.
Value [in]
The value to send to the device.

Returns

LJM errorcodes or 0 for no error.

Remarks

For an alternate function using an address rather than name, see LJM_eWriteAddress. More code examples coming soon.

Example

[C/C++] Write a value of 2.5V to the DAC0 analog output

int LJMError;

// handle comes from LJM_Open()
LJMError = LJM_eWriteName(handle, "DAC0", 2.5);
if (LJMError != LJME_NOERROR) {
    // Deal with error
}

2.2.2 - eReadName

Read one value, specified by name.

Syntax

LJM_ERROR_RETURN LJM_eReadName(
                      int Handle,
                      const char * Name,
                      double * Value)

Parameters

Handle [in]
A device handle. The handle is a connection ID for an active device. Generate a handle with LJM_Open or LJM_OpenS.
Name [in]
The name that specifies the Modbus register(s) to read.  Names can be found throughout the device datasheet or in the Modbus Map.
Value [out]
The value returned from the device.

Returns

LJM errorcodes or 0 for no error.

Remarks

For an alternate function using an address rather than name, see LJM_eReadAddress. More code examples coming soon.

Example

[C/C++] Read the serial number of the device.

int LJMError;
double newValue;

// handle comes from LJM_Open()
LJMError = LJM_eReadName(handle, "SERIAL_NUMBER", &newValue);
if (LJMError != LJME_NOERROR) {
    // Deal with error
}
printf("SERIAL_NUMBER: %f\n", newValue);

2.2.3 - eWriteAddress

Write one value, specified by address.

Syntax

LJM_ERROR_RETURN LJM_eWriteAddress(
                      int Handle,
                      int Address,
                      int Type,
                      double Value)

Parameters

Handle [in]
A device handle. The handle is a connection ID for an active device. Generate a handle with LJM_Open or LJM_OpenS.
Address [in]
The address that specifies the Modbus register(s) to write. Addresses can be found throughout the device datasheet or in the Modbus Map.
Type [in]
The data type of the value:
Type LJM Constant Name LJM Constant Value
unsigned 16-bit integer LJM_UINT16 0
unsigned 32-bit integer LJM_UINT32 1
signed 32-bit integer LJM_INT32 2
floating point 32-bit LJM_FLOAT32 3
Value [in]
The value to send to the device. The input data type is a double, and will be converted according to the Type input.

Returns

LJM errorcodes or 0 for no error.

Remarks

For an alternate function using a name rather than address, see LJM_eWriteName.

Examples

[C/C++] Write a value of 2.5V to the DAC0 analog output.

int LJMError;

// handle comes from LJM_Open()
LJMError = LJM_eWriteAddress(handle, 1000, 3, 2.5);
if (LJMError != LJME_NOERROR) {
    // Deal with error
}

2.2.4 - eReadAddress

Read one value, specified by address.

Syntax

LJM_ERROR_RETURN LJM_eReadAddress(
                      int Handle,
                      int Address,
                      int Type,
                      double * Value)

Parameters

Handle [in]
A device handle. The handle is a connection ID for an active device. Generate a handle with LJM_Open or LJM_OpenS.
Address [in]
The address that specifies the Modbus register(s) to read. Addresses can be found throughout the device datasheet or in the Modbus Map.
Type [in]
The data type of the value:
Type LJM Constant Name LJM Constant Value
unsigned 16-bit integer LJM_UINT16 0
unsigned 32-bit integer LJM_UINT32 1
signed 32-bit integer LJM_INT32 2
floating point 32-bit LJM_FLOAT32 3
Value [out]
The value returned from the device. The output data type is a double, and will be converted according to the Type input.

Returns

LJM errorcodes or 0 for no error.

Remarks

For an alternate function using a name rather than address, see LJM_eReadName.  More code examples coming soon.

Examples

[C/C++] Read the serial number of the device.

int LJMError;
double newValue;

// handle comes from LJM_Open()
LJMError = LJM_eReadAddress(handle, 60028, 1, &newValue);
if (LJMError != LJME_NOERROR) {
    // Deal with error
}
printf("SERIAL_NUMBER: %f\n", newValue);

2.2.5 - eWriteNameString

Writes a string, specified by name.

Syntax

LJM_ERROR_RETURN LJM_eWriteNameString(
                      int Handle, 
                      const char * Name, 
                      const char * String)

Parameters

Handle [in]
A device handle. The handle is a connection ID for an active device. Generate a handle with LJM_Open or LJM_OpenS.
Name [in]
The name that specifies the Modbus string-type register to write.  Names can be found throughout the device datasheet or in the Modbus Map.
String [in]
The string to write. Must null-terminate at size LJM_STRING_ALLOCATION_SIZE (50) or less.  

Returns

LJM errorcodes or 0 for no error.

Remarks

See also LJM_eReadNameString. This is a convenience function that uses LJM_eNames. Only for use with Modbus register(s) listed as type LJM_STRING (98). More code examples coming soon.

Examples

[C/C++] Change the device name.

int LJMError;
// LJM_STRING_ALLOCATION_SIZE is 50
char newName[LJM_STRING_ALLOCATION_SIZE] = "My Favorite DAQ Device";

// handle comes from LJM_Open()
LJMError = LJM_eWriteNameString(handle, "DEVICE_NAME_DEFAULT", newName);
if (LJMError != LJME_NOERROR) {
    // Deal with error
}

2.2.6 - eReadNameString

Reads a string, specified by name.

Syntax

LJM_ERROR_RETURN LJM_eReadNameString(
                      int Handle, 
                      const char * Name, 
                      char * String)

Parameters

Handle [in]
A device handle. The handle is a connection ID for an active device. Generate a handle with LJM_Open or LJM_OpenS.
Name [in]
The name that specifies the Modbus string-type register to read.  Names can be found throughout the device datasheet or in the Modbus Map.
String [out]
A string that is updated to contain the result of the read. Must be allocated to size LJM_STRING_ALLOCATION_SIZE (50) or greater prior to calling this function.

Returns

LJM errorcodes or 0 for no error.

Remarks

See also LJM_eWriteNameString. This is a convenience function that uses LJM_eNames. Only for use with Modbus register(s) listed as type LJM_STRING (98).

Examples

[C/C++] Read the device name.

int LJMError;
// LJM_STRING_ALLOCATION_SIZE is 50
char devName[LJM_STRING_ALLOCATION_SIZE];

// handle comes from LJM_Open()
LJMError = LJM_eReadNameString(handle, "DEVICE_NAME_DEFAULT", devName);
if (LJMError != LJME_NOERROR) {
    // Deal with error
}
printf ("%s \n", devName);

2.2.7 - eWriteAddressString

Writes a string, specified by address.

Syntax

LJM_ERROR_RETURN LJM_eWriteAddressString(
                      int Handle, 
                      int Address, 
                      const char * String)

Parameters

Handle [in]
A device handle. The handle is a connection ID for an active device. Generate a handle with LJM_Open or LJM_OpenS.
Address [in]
The address that specifies the Modbus string-type register to write.  Addresses can be found throughout the device datasheet or in the Modbus Map.
String [in]
The string to write. Must null-terminate at size LJM_STRING_ALLOCATION_SIZE (50) or less.  

Returns

LJM errorcodes or 0 for no error.

Remarks

See also LJM_eReadAddressString. This is a convenience function that uses LJM_eAddresses. Only for use with Modbus registers listed as type LJM_STRING (98). More code examples coming soon.

Examples

[C/C++] Change the device name.

int LJMError;
// LJM_STRING_ALLOCATION_SIZE is 50
char newName[LJM_STRING_ALLOCATION_SIZE] = "My Favorite DAQ Device";

// handle comes from LJM_Open()
LJMError = LJM_eWriteAddressString(handle, 60500, newName);
if (LJMError != LJME_NOERROR) {
    // Deal with error
}

2.2.8 - eReadAddressString

Reads a string, specified by address.

Syntax

LJM_ERROR_RETURN LJM_eReadAddressString(
                      int Handle, 
                      int Address, 
                      char * String)

Parameters

Handle [in]A device handle. The handle is a connection ID for an active device. Generate a handle with LJM_Open or LJM_OpenS.

Name [in]
The address that specifies the Modbus string-type register to read.  Addresses can be found throughout the device datasheet or in the Modbus Map.
String [out]
A string that is updated to contain the result of the read. Must be allocated to size LJM_STRING_ALLOCATION_SIZE (50) or greater prior to calling this function.

Returns

LJM errorcodes or 0 for no error.

Remarks

See also LJM_eWriteAddressString. This is a convenience function that uses LJM_eAddresses. Only for use with Modbus registers listed as type LJM_STRING (98).

Examples

[C/C++] Read the device name.

int LJMError;
// LJM_STRING_ALLOCATION_SIZE is 50
char devName[LJM_STRING_ALLOCATION_SIZE];

// handle comes from LJM_Open()
LJMError = LJM_eReadAddressString(handle, 60500, devName);
if (LJMError != LJME_NOERROR) {
    // Deal with error
}
printf ("%s \n", devName);