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DOIO
The DO I/O (DOIO) function is used to update inputs or outputs for one scan while the program is running. The DOIO function can also be used to update selected I/O during the program in addition to the normal I/O scan.
If input references are specified, the function allows the most recent values of inputs to be obtained for program logic. If output references are specified, DO I/O updates outputs based on the most current values stored in I/O memory. I/O is serviced in increments of entire I/O modules; the PLC adjusts the references, if necessary, while the function executes.
The DOIO function has four input parameters and one output parameter. When the function receives power flow and input references are specified, the input points at the starting reference (ST) and ending at END are scanned. If a reference is specified for ALT, a copy of the new input values is placed in memory, beginning at that reference, and the real input points are not updated. ALT must be the same size as the reference type scanned. If a discrete reference is used for ST and END, then ALT must also be discrete. If no reference is specified for ALT, the real input points are updated.
When the DOIO function receives power flow and output references are specified, the output points at the starting reference (ST) and ending at END are written to the output modules. If outputs should be written to the output modules from internal memory, other than %Q or %AQ, the beginning reference can be specified for ALT. The range of outputs written to the output modules is specified by the starting reference (ST) and the ending reference (END).
Execution of the function continues until either all inputs in the selected range have reported, or all outputs have been serviced on the I/O cards. Program execution then returns to the next function following the DO I/O.
If the range of references includes an option module (HSC, APM, etc.), then all of the input data (%I and %AI) or all of the output data (%Q and %AQ) for that module will be scanned. The ALT parameter is ignored while scanning option modules. Also, the reference range must not include an Enhanced GCM module (see Note below).
Note
For Release 9.0 and later CPUs, the DOIO function can be used with an
Enhanced GCM module.
Chapter 4 Series |
