Moka7 Multivar - Byte - FillByte

[Martin Hinrichs]

Hi,

I am integrate the multivar Function in Moka7 and i am testing now.
Now i found a problem where dont find a solution.

Datatypes with 2bytes or 4bytes are running good.
But if try to read/write a byte wrapped in a Telegramm with multiple items. The protocol fills up the data-parameter with 1 byte. o_O

This picture show my Problem.
http://i60.tinypic.com/zsnjr.jpg

Parameter: (Write Var)
..
..
Item [3]: (DB101.DBX 10.0 BYTE 1)
Variable specification: 0x12
Length of following address specification: 10
Syntax Id: S7ANY (0x10)
Transport size: BYTE (2)
Length: 1
DB number: 101
Area: Data blocks (DB) (0x84)
Address: 0x000050
..
..
Data
..
..
Item [3]: (Reserved)
Return code: Reserved (0x00)
Transport size: BYTE/WORD/DWORD (0x04)
Data length: 1 Bytes
Data: 01
Fill byte: 0x00 <<--

So every follow item get in trouble with this filling byte.
It seems there a minimum Size (2bytes) for the Data. But i cant believe.

[Davide Nardella]

"It seems there a minimum Size (2bytes) for the Data. But i cant believe"
You are almost near ;)

You have this problem for all odd amount of byte (non only for 1 byte).
The protocol requires that every block (except for the last one) must contain an even number of bytes.
So, if the amount is odd, you need to add a padding byte.

[Martin Hinrichs]

Thats a really good answer. So i can fix it.

I thought i can use it to read/write booleans on Siemens Devices.

I could set the transport size to "Bit".
But there are some unknow fields for me like start-adress and the length which is in byte So i think the protocol reserved also 1 byte and i have the problem with even byte again.

Have Snap7 a Solution to write a Single Bit?

[Davide Nardella]

Yes, you can read/write a single bit, it is transferred as 1 byte.
Yes, the data amount must be even.

You need to add a further input int param : the wordLength.

Add these constant in do S7 class

public static final int WLBit = 0x01;
public static final int WLByte = 0x02;
public static final int WLTimer = 0x1D;
public static final int WLCounter = 0x1C;

The WordLength must be copied in PDU[22].

Then modify this:

        // Adjusts Start and word length
        if ((Area==S7.S7AreaCT) || (Area==S7.S7AreaTM))
        {
            Address = Start;
            Length = DataSize;
            if (Area==S7.S7AreaCT)
                PDU[22]=S7WLCounter;
            else
                PDU[22]=S7WLTimer;
        }
        else
        {
            Address = Start<<3;
            Length  = DataSize<<3;
        }

to:

        PDU[22]=WordLength;
        // Adjusts Start and word length
        if ((WordLength==S7.WLBit) || (WordLength==S7.WlTimer) || (WordLength==S7.WlCounter))
        {
            Address = Start;
            Length = DataSize;
        }
        else
        {
            Address = Start<<3;
            Length = DataSize<<3;
        }

These are untested.

For address calc refer to my email of (20/9/2014), I already explained you.

For other infos about fields, please refer to C++ sources (s7_types.h)