GE 90-30/20/Micro MCR

4-124 Series 90-30/20/Micro Programmable Controllers Reference Manual – September 1998 GFK-0467K

MCR

All rungs between an active Master Control Relay (MCR) and its corresponding End Master

Control Relay (ENDMCR) function are executed without power flow to coils. An ENDMCR

function associated with the MCR is used to resume normal program execution. Unlike the JUMP

instruction, MCRs can only occur in the forward direction. The ENDMCR instruction must appear

after its corresponding MCR instruction in a program.

Logicmaster 90-30/20/Micro software supports two forms of the MCR function, a non-nested and a

nested form. The non-nested form has been available since Release 1 of the software, and has the

name MCR.

Note

The 350 and 360 series CPUs do not have the non-nested form, i.e., MCR. Use

only the nested form, i.e., MCRN with 350 and 360 series CPUs.

There can be only one MCR instruction for each ENDMCR instruction. The range for non-nested

MCRs and ENDMCRs cannot overlap the range of any other MCR/ENDMCR pair or any

JUMP/LABEL pair of instructions. Non-nested MCRs cannot be within the scope of any other

MCR/ENDMCR pair or any JUMP/LABEL pair. In addition, a JUMP/LABEL pair or an

MCR/ENDMCR pair cannot be within the scope of an MCR/ENDMCR pair.

Note

The non-nested MCR function is the only Master Control Relay function that can

be used in a Release 1 Series 90-30 PLC. The nested MCR function should be

used for all new applications.

The nested form of the MCR function has the name MCRN, and is available in Release 2 and later

releases of the Series 90-30 PLC. An MCRN function can be nested with other MCRN functions,

provided they are nested correctly. An MCRN instruction and its corresponding ENDMCRN

instruction must be contained completely within another MCRN/ENDMCRN pair.

An MCRN function can be placed anywhere within a program, as long as it is properly nested with

respect to other MCRNs, and does not occur in the range of any non-nested MCR or non-nested

JUMP.

Note

Use only one (1) MCRN for each ENDMCRN with 350 and 360 series CPUs.

There can be multiple MCRN functions corresponding to a single ENDMCRN (except for the 350

and 360 series CPUs as noted above). This is analogous to the nested JUMP, where you can have

multiple JUMPs to the same LABEL. For differences between the JUMP function and the MCR

function, refer to the “Differences Between MCRs and Jumps” section on page 4-125.