We are running a survey to help us improve the experience for all of our members. If you see the survey appear, please take the time to tell us about your experience if you can.
HEy we have designed our own 8051 board using 4066 to convert single serial port to 4 port but gives lots of garbage once we power up
OK, it may 'work' but it does not WORK. For one thing, when mistakenly using an analog switch for logical signals, resistors are required to keep the floating pins in a steady state (in this case high).
That something 'works' does not mean that it WORKS. My most rewarding jobs has been to fix stuff that 'works'.
Erik
I must have been unclear, when I recommended pdf or some image format. I made the suggestion to make sure that it would be easy for people to view any uploaded information. Alas, I don't have a Word reader on my phone. Another thing is that a lot of people are a bit weary of opening word documents received from unknown sources, since M$ in their infinite wisdom made *.doc capable of hosting virus.
From Eriks comment I have to ask - is your uploaded schematic before - or after - you added your pull-up resistors? It sounds like they are missing in your schematic.
in this schematic where no pullups are added please tell me where to add pullups in this schematic. I will upload pdf format of schematic... and will send u URL soon...
please check the following URL... www.sendspace.com/.../m2agng
will send u URL soon... ... please understand that this is a professional forum and treat it as such. This is not two teenagers texting each other.
please tell me where to add pullups in this schematic. No MAX232(equivalent) transmit logical inputs may never float
... please understand that this is a professional forum and treat it as such. This is not two teenagers texting each other.
No MAX232(equivalent) transmit logical inputs may never float.
Horrible double negative make sentences very difficult to understand.
MAX232(equivalent) transmit logical inputs may never float.
Thanks for the observation
Not a "Horrible double negative" but a mistake
That's OK. I forgive you ;)
As I have already noted, every logic level input on the MAX232 chips must have a known state.
Your 4066 will sometimes connect the corresponding processor pin output to the MAX232 making the logic level known. But the corresponding inputs on the other MAX232 chips will then be left floating when the 4066 gates changes to high-impedance.
So add resistors on every single logic-level input of every single MAX232. Note that I am talking about logic-level input, so not the side to the outside world. And not the data direction where the MAX232 sends data to the microprocessor, but the signals where data comes (or may come) from processor and enter the MAX232.
By the way - did you intend to run your design with separate multiplexing for receive and transmit? If not, then you can manage with half the number of port pins for controlling the multiplexing.