Saturday, August 13, 2011

Memory Area of Omron CP1H PLCs

Memory area of PLC is the allocation of internal memory PLC that is accesible to be used as an operand of an instruction. Before learning the PLC programming technique. For PLC programmer, understanding the memory area of PLC is a must.
In this chapter, Omron CP1H is used as the example. This is fairly representative, due to the other series is similar. Likewisw for the other brands are basically the same principle.
In the memory area of Omron CP1H consists CIO area, Work area(W), Holding area(H), Auxiliary area(A), DM area(DM), Timer(T), Counter(C), Task flag area(TK), Data registers(DR), Index registers(IR), Condition flag area, and Clock pulse area.

The following table is a memory allocation for Omron CP1H. For example by knowing the allocations, it will be known to the allocation of operands that can be used, or operands that stiil keep even if power of PLC is off.
I/O Memory area CP1H by Omron

I/O Memory area CP1H by Omron

From the table above can be explained as follows:
1. Common Input Output area (CIO)
Generally used as data exchanges such as I/O refresing with PLC units. Words that  are not allocated to unit can be used as work words or work bits on program.
CIO Memory Area Omron CP1H 

2. Work Area (W)
This area is used as programming. Words in this work area can be used for programming and can not be used for I/O exchanged with external I/O terminal.
3. Holding Area (H)
Words in this Holding area can be used for programming. They will retain the status when PLC is turned ON or the operating mode is changed (Program-Monitor-Run).
4. Auxiliary Area (A)
These words are allocated to specific functions in the system, so it can not be used for programming or read only. example is for program date.
5. Temporarry Relay Area (TR)
TR area is used to record the status of program branches.
6. Data Memory Area (D)
It is multi purpose data area that normally accessed only in words. The contains of these words retain although PLS switch ON-OFF or operation mode is changed (Program-Monitor-Run).
7. Timer/Counter Area
This timer number is T0 to T4095
8. Condition flags
This flags contan arithmatic flags, such as error flag, equal flag, always On, Always Off. etc.
9. Clock Pulses 
On and Off by the  internal timer of CPU.

10. Task Flag Area (TK)
This flag status for corresponding cyclic task.
11. Index Registers (IR)
Used to store memory address. It is IR0 to IR15.
12. Data Register (DR)
Used togather with IR. It is DR DR0 to DR15.

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