Siemens NAN 67 Series Manual de Serviço descarregar pdf (Página 247)

20-13

Ladder Logic (LAD) for S7-300 and S7-400

C79000-G7076-C504-02

RLO

MSP !

MCRA MCRD10

RLO Pushed bit

MSP = MCR stack pointer

MA = Bit for controlling MCR-dependency

Pushed bit 1

Figure 20-7 Master Control Relay Stack

The instructions ––(MCR<) and ––(MCR>) must always be used in pairs

within your program.

The instruction ––(MCR<) takes over the signal state of the RLO and copies

it to the MCR bit.

The instruction ––(MCR>) sets the MCR bit absolutely to 1. Because of this

characteristic, every other instruction between the instructions ––(MCRA)

and ––(MCRD) operates independent of the MCR bit (for information on

––(MCRA) and ––(MCRD), see above).

You can nest the instructions ––(MCR<) and ––(MCR>). The maximum

nesting depth is eight, i.e. you can write a maximum of eight ––(MCR<)

instructions one after the other before inserting an ––(MCR>) instruction.

You must program an equal number of ––(MCR<) and ––(MCR>)

instructions.

If the ––(MCR<) instructions are nested, the MCR bit of the lower nesting

level is formed. The ––(MCR<) instruction then links the current RLO with

the current MCR bit in accordance with the AND truth table.

When an ––(MCR>) instruction finishes a nesting level, it fetches the MCR

bit from the next higher level.

Nesting the

Instructions

(MCR<) and

(MCR>)

Program Control Instructions

1 2 ... 242 243 244 245 246 247 248 249 250 251 252 ... 317 318

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Siemens NAN 67 Series Manual de Serviço Página 247