FCMND program instruction FCMND program instruction Syntax FCMND (logical_unit, command_code) $out_string, $in_string Function Generate a device-specific command to the input/output device specified by the logical unit. Usage Considerations The logical unit referenced must have been previously attached. As appropriate, the current default device, unit, and directory path are considered for any disk file specification (see the DEFAULT command). Parameters logical_unit Real-valued expression that identifies the device to be accessed. (See the ATTACH instruction for a description of logical unit numbers.) command_code Real-valued expression that specifies the command to be executed.
(See the explanation of command codes below.) $out_string String constant, variable, or expression that is transmitted to the device along with the command code to specify the operation to be performed. $in_string Optional string variable. This variable receives any information returned from the device as a result of the command. Details This instruction allows a program to generate device-specific command sequences. For example, this instruction can be used to send a command to the disk to delete a file or to rename a file.
Since these are maintenance operations, which are not generally performed by eV+ programs, no special-purpose eV+ program instructions exist for performing these operations. Any error in the specification of this instruction (such as attempting to access an invalid unit) will cause a program error and will halt program execution. However, errors associated with performing the actual operations (such as device not ready) do not halt program execution since these errors can occur in the normal operation of a program. These normal errors can eV+Language Reference Guide, v2.x, 18319-000 Rev A Page 219