Write, single bit example

[cropii]

Hello i read bit like this, bud i can't change it and write back.

i got 100.1 100.2 they are false i need change it to true and write it back. s7client.MBRead(100, 1, function(err, buffer) { if(err) return console.log(' >> MBRead failed. Code #' + err + ' - ' + s7client.ErrorText(err)); var bit=(buffer[0] & 0x01)!=0;

        console.log(bit); // say's false.

});

Some one please help me to write function that will change bit and write it back

[mathiask88]

Hi,

if you want to write only a single bit you have to use S7Client.WriteArea(area, dbNumber, start, amount, wordLen, buffer, [callback]) with wordLen=S7WLBit.

For example if you want to change M100.1 to true:

var snap7 = require('node-snap7');

var s7client = new snap7.S7Client();
s7client.ConnectTo('127.0.0.1', 0, 1, function(err) {
    if(err)
        return console.log(' >> Connection failed. Code #' + err + ' - ' + s7client.ErrorText(err));

    // Change M100.1 to true
    s7client.WriteArea(s7client.S7AreaMK, 0, (100*8+1), 1, s7client.S7WLBit, new Buffer([0x01]), function(err) {
        if(err)
            return console.log(' >> WriteArea failed. Code #' + err + ' - ' + s7client.ErrorText(err));
    });
});

[cropii]

thank you!!! it's work's !

bud now when i read i any way get false in my function maybe i do somting wrong when read bit?

[mathiask88]

In your given example you read the full merker byte M100 but you test for the first bit with 0x01 but M100.1 is the second bit and M100.2 the third. So you have to do var bit = !!(buffer[0] & 0x02) for M100.1 and var bit = !!(buffer[0] & 0x04) for M100.2.

[cropii]

And again thank you!