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.

LJM_eWriteName - Write one value specified, by name.
LJM_eReadName - Read one value specified, by name.
LJM_eWriteNameString - Write one string value, specified by name.
LJM_eReadNameString - Read one string value, specified by name.

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.

LJM_eWriteAddress - Write one value, specified by address/type.
LJM_eReadAddress - Read one value, specified by address/type.
LJM_eWriteAddressString - Write one string value, specified by address.
LJM_eReadAddressString - Read one string value, specified by address.

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);