Description
This is the main function to read
data from a PLC.
With it you can read DB, Inputs, Outputs, Merkers, Timers and Counters.
Declaration
int ReadArea(int Area, uint16_t DBNumber, uint16_t Start,
uint16_t Amount, void *pUsrData);
Parameters
|
|
Type |
Dir. |
Mean |
|
Area |
int |
In |
Area identifier. |
|
DBNumber |
uint16_t |
In |
DB Number if Area = S7AreaDB, otherwise is ignored. |
|
Start |
uint16_t |
In |
Offset to start |
|
Amount |
uint16_t |
In |
Amount of words to read (1) |
|
pUsrData |
Pointer to memory area |
In |
Address of user buffer. (see remarks) |
(1) Note the use of the parameter name “amount”, it means quantity of words, not byte size.
Area table
|
|
Value |
Mean |
|
S7AreaPE |
0x81 |
Process Inputs. |
|
S7AreaPA |
0x82 |
Process Outputs. |
|
S7AreaMK |
0x83 |
Merkers. |
|
S7AreaDB |
0x84 |
DB |
|
S7AreaCT |
0x1C |
Counters. |
|
S7AreaTM |
0x1D |
Timers |
Return value
· 0 : The function was accomplished with no errors.
· Other values : see the Errors Code List.
Remarks
As said, every data packet exchanged with a PLC must fit in a PDU, whose size is fixed and is 240 bytes for this implementation of Settimino.
If this data size exceeds the PDU size, the packet is automatically split across more subsequent transfers and your buffer should be large enough to receive the data.
If NULL is passed as pUsrData, the data remains into the PDU buffer and the size requested is trimmed to the max (222 bytes).
This allow to save memory avoiding to supply a further memory buffer if you plan to make only small data transfers.
The parameter Amount is not the size in bytes.
Particularly:
Buffer size (byte) = Word size * Amount
Where:
|
|
Word size |
|
(E/A/M/DB) - Byte |
1 |
|
Counter |
2 |
|
Timer |
2 |