RS485 without a 555

[Ioannis]

Do you mean that your data are always 1?

If it is, then sure youdo not need the 555. But what kind of data is always 1? Power supply?

Ioannis

[The Master]

The data isnt always 1. When the TX pin goes low then the RS485 chip resets back to a receiver so the line goes low

[Ioannis]

If the data line retuns to zero,that does not mean end of transmission. Do not get confussed.

End of transmissions happens some time later. This "later" gives the 555 as a monostable multivibrator.

Ioannis

[The Master]

What exactly is this "end of transmission"? I thought it was either on or off

[Ioannis]

I believe there is a problem with the basics here.

E.g. you have to send the following byte:

1 1 1 0 0 1 1 0

You send all the bits and not the '1's only

The RE and DE (if connected together) must be at high level before the first bit and a little after the last bit.

Ifyou send with a baud rate of 9600, then each bit is 1/9600=0,1042msec nd the full 8+2 bits (Start and Stop) will be 1,042msec. So the RE and DE have to be more than 1,042 msec high. Not just for the time that a bit of the data is 1.

Is that more clear now?

Ioannis

[The Master]

Yes, I understand what your saying but i dont understand why. The value can only be 1 or 0. When the 485 chip is in receiver mode then isnt that a 0?

[Ioannis]

What value?

You have a control input (Send or Receive) and a couple of data input/output.

When you send data, regardless if it is 1 or 0, you make control input high. This input is control not data. Your data can be 1 or 0. When you are done with data, then control input is set to low again, and you are ready to get any valid data.

In reallity the chip has 2 control pins and 2 data pins. Control are anti phase active so you can connect them together. Data can only be sent or received. Not at the same time if you have only one couple of lines (A-B), so you can connect data in and data out together too.

Ioannis