About write bit to DB address

[sunblack110]

Hi Robinson,

I have a small question, as I would like to write a bit to PLC , but seems that I didn't see any function which is able to fit my requirement.

But I saw that we have the bit type for write, but the method is private.

//writeArea write generic area into PLC with following parameters: //1.area: s7areape/s7areapa/s7areamk/s7areadb/s7areact/s7areatm //2.dbnumber: specify dbnumber, to use in write DB area, otherwise = 0 //3.start: start of the address //4.amount: amount of the address //5.wordlen: bit/byte/word/dword/real/counter/timer //6.buffer: a byte array input for writing func (mb *client) writeArea(area int, dbnumber int, start int, amount int, wordlen int, buffer []byte) (err error) { var address, numElements, maxElements, totElements, dataSize, isoSize, length int

5.wordlen: bit/byte/word/dword/real/counter/timer

I would like to know why don't we export the function or create a WriteBit function?

For this case, I need to work around it to read the byte first , then change one bit , and write back , but it's not good way as it will take more time to do it .

Do you have any plan to fix this issue or have any other idea about this ?

Thanks,
Han

[robinson]

Hi Han,
in fact writing bit is a set Boolean function, you can refer at:

gos7/helper.go

Line 323 in fa6e769

func (s7 *Helper) SetBoolAt(b byte, bitPos uint, data bool) byte {

Br, Robinson

[sunblack110]

Hi robinson,

Thanks for you quickly response . I noticed this function you mean. But this is a only a memory operation to avoid change the old values in this byte, but we need to read the old value first from PLC . I think it's not good way to do it .

Not sure if I make myself clear or not.

Thanks,
Han

[cookedsteak]

@sunblack110 Here is the solution, you can add a Method such as

func (mb *client) AGWriteDBBit(dbNumber int, start int, size int, buffer []byte) (err error) {
	return mb.writeArea(s7areadb, dbNumber, start, size, s7wlbit, buffer)
}

Just change the parameter s7wlbyte into s7wlbit.

[jwzl]

In reality, it seems that s7wlbit is not work and just read and write a byte is okay for change a bit.