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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
1kohm is a quite strong pull - 5mA at 5V.
And by the way - where did you place the resistors? Remember that we still haven't seen your exact schematics, and the RX and TX signals are avaiable at several different points through the construction. Both as RS232 level signals on the outside of the RS232 transceiver, and directly on the inside of the RS232 transceiver and on the inside of your mux design, directly at the processor pins.
And since the signals have different data direction, the resistors should be placed at different positions in the circuit for the RX signal compared to the TX signal since the pull-up is intende to help with stable logic states for the logic input sides of the signals in case there isn't an active driver that can make sure that the signal has distinct high or distinct low level.
Hey I want to send schematic but how to send.....
if can give me your mail id I will forward it.
I think I get just enough with spam without adding my mail address on a frequently scanned forum page.
Upload the schematics - preferably as pdf or an image - to a file or image hosting site and then post a link.
This is a public forum, which means that the debate should be made in public where everyone have a chance to participate. The main alternative is private tutoring or consultants.
please find schematic at follwoing URL----
www.sendspace.com/.../gpa5w6
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.