Mitsubishi MELSEC A PLCs store device (point) data in areas of memory known as Device memory, Buffer memory, and Register memory. You use the Device field on the Mitsubishi Scanner Form to define the area of memory that a particular scanner is to scan. You then use further fields on the Mitsubishi Scanner Form to define the particular address range that is to be scanned within that area of memory, and fields on the Mitsubishi Point Forms to define the particular address(es) that are associated with each point.
Mitsubishi MELSEC A PLCs allocate device (point) data in Words or Bits, depending on the area of memory in which it the data is located in the PLC. You need to be aware of which unit (Word or Bit) is associated with each area of memory, in order to configure the location of the point data correctly within the Geo SCADA Expert database. (Be aware that Geo SCADA Expert retrieves a minimum of one Word of data, regardless of the PLC memory area in which the source data is located.)
The table below lists the areas of memory in each type of PLC. It also indicates whether the data in each area is allocated in Bits or Words, and the ranges that are associated with each area of memory.
| Memory Allocation in Mitsubishi MELSEC A PLCs | ||||
|---|---|---|---|---|
|
Device |
ACPU Range |
AnACPU Range |
Addressing Convention |
Unit |
|
Link Relay B |
B0000 to B03FF |
B000000 to B000FFF |
Hexadecimal |
Bit |
|
Counter (Present Value) C |
CN000 to CN255 |
CN00000 to CN01023 |
Decimal |
Word |
|
Data Register D |
D0000 to D1023 |
D000000 to D006143 |
Decimal |
Word |
|
Special Register D |
D9000 to D9255 |
D009000 to D009255 |
Decimal |
Word |
|
Annunciator F |
F0000 to F0255 |
F000000 to F002047 |
Decimal |
Bit |
|
Latch Relay L |
L0000 to L2047 |
L000000 to L008191 |
Decimal |
Bit |
|
Internal Relay M |
M0000 to M2047 |
M000000 to M008191 |
Decimal |
Bit |
|
Special Relay M |
M9000 to M9255 |
M009000 to M009255 |
Decimal |
Bit |
|
File Register R |
R0000 to R8191 |
R000000 to R008191 |
Decimal |
Word |
|
Step Relay S |
S0000 to S2047 |
S000000 to S008191 |
Decimal |
Bit |
|
Timer (Present Value) T |
TN000 to TN255 |
TN00000 to TN02047 |
Decimal |
Word |
|
Link Register W |
W0000 to W03FF |
W000000 to W000FFF |
Hexadecimal |
Word |
|
Input X |
X0000 to X07FF |
X000000 to X0007FF |
Hexadecimal |
Bit |
|
Output Y |
Y0000 to Y07FF |
Y000000 to Y0007FF |
Hexadecimal |
Bit |
In addition to the above, Geo SCADA Expert can also read and write to the Buffer memory in a MELSEC A PLC. For details of the address allocations for Buffer memory, see the Mitsubishi documentation supplied with the MELSEC A PLCs.
For examples showing how to specify and display PLC memory address ranges within Geo SCADA Expert, see Configuration Examples.
Further Information