GE 90-30/20/Micro manual Svcreq, Service Request Functions

4

SVCREQ

Use the Service Request (SVCREQ) function to request one of the following special PLC services:

Table 4-3. Service Request Functions

Function	Description
1	Change/Read Constant Sweep Timer.
2	Read Window Values.
3	Change Programmer Communications Window Mode and Timer Value.
4	Change System Comm. Window Mode and Timer Value.
6	Change/Read Checksum Task State and Number of Words to Checksum.
7	Change/Read Time-of-Day Clock.
13	Shut Down the PLC.
14	Clear Fault Tables.
15	Read Last-Logged Fault Table Entry.
16	Read Elapsed Time Clock.
18	Read I/O Override Status.
23	Read Master Checksum
26/30	Interrogate I/O
29	Read Elapsed Power Down Time

The SVCREQ function has three input parameters and one output parameter. When the SVCREQ receives power flow, the PLC is requested to perform the function FNC indicated. Parameters for the function begin at the reference given for PARM. The SVCREQ function passes power flow unless an incorrect function number, incorrect parameters, or out-of-range references are specified. Additional causes for failure are described on the pages that follow.

The reference given for PARM may represent any type of word memory (%R, %AI, or %AQ). This reference is the first of a group that make up the “parameter block” for the function. Successive 16-bit locations store additional parameters. The total number of references required will depend on the type of SVCREQ function being used.

Parameter blocks may be used as both inputs for the function and the location where data may be output after the function executes. Therefore, data returned by the function is accessed at the same location specified for PARM.

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(enable)(ok)

REQ

(service number) —FNC

(beginning reference)-PARM

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4-132 Series 90-30/20/Micro Programmable Controllers Reference Manual–September 1998 GFK-0467K