No, it is tri-state. That means you have the option to drive it bi-directionally or to put in into tri-state which is a very high impedance and it will appear as an open circuit.Hi Space varmit, this look like it's what I need however will this force this line low/high I cannot see any specs on sink and source currents. I was going re-post / change my question to remove the ambiguity regarding RS232, my altered post was going read like this if it makes clearer.
I have a MCU pin that toggles tetween 0-5v at fairly low speeds (<10khz) This pin is connected via open collector transistos so as not to affect the line when not is use, the line is pulled high (5v) extrenally and other MCU's are connected using same method. Data is then sent down this so the MCU's can talk
I want to have this method but also an "override method" so when my pin goes high the line it is kept high and cannot be pulled low by other MCU's and vice versa for low. This override methoed needs to be switchable (on/off)
The current needed to force the line high is a few ma, I need to measure the current required to force the line low but suspect it to be <100ma
P.S. thanks for the hlep so far.
With bipolar trnasistors you can prevent another transmitter from getting a message through. The other transmitter can do the same thing to you. Listen carefully. You cannot override the other transmitters signal unless it is passively pulled up. This signaling mechanism has nothing whatever to with RS-232 so quit bringing that term into the discussion, it is just confusing things.All the RS232 levels are same (TTL)
All devices are connected via bipolar transistors
my current circuit connects via bipolar transistors so as not to cause problems
I want to sometimes take control of the single wire and FORCE my Tx on it, ensuring nothing else on bus overrides it (don't forget they are connected via bipolar)
I'm sure this can be done as I have forced a low (holding wire to GND) and forced a HI holding wire to 5v, but I'm looking for a simple way if switching this on / off
And for all of your bluster and righteous indignation, the fact remains that there is no way to reliably communicate on a point to point link, such as you have described, with two transmitters which are capable of mutually interfereing with each other.PapaBravo
You obviously did not read my post before having a go at me, if you read it I said exactly what you said and that is talking about RS232 was causing confusion so I removed it, it might help if you read posts before having a go at a newbie. also when I have asked questions in the past people say "tell us everything" in this case I'm told not to! very confusing.
Now it might be my terminology or lack of knowledge but all I know is if I stick the line direct to GND no data appears on the line and if I stick it to 5v supply again no data just flat 5v line. so it is possible to override the signals, how would I do this "forcing" in time with a pulse on a pin even if this some sort of power transistor, one for GND and one for 5v.
Thx in advance to all those helping.
lol.... he was a bit harsh with you.And for all of your bluster and righteous indignation, the fact remains that there is no way to reliably communicate on a point to point link, such as you have described, with two transmitters which are capable of mutually interfereing with each other.
OK, so you are not trying to block a comm signal from getting through to another point? I though you had two devices communicating with each other and you needed to gate open the signal path in which case the '373 would have worked nicely. But you want the power lifted with the MPU signal? Correct? If so, then you need a transistor switch. You can do that both ways either by apply VCC through a transistor or GND through a transistor. If the MCU is separate from the comm chip power then no problem.I know, but as he appears not to want to help I'm just going to ignore it however I think he believes all devices are of the same specification and therefore no matter what I do you could never achieve what I want, I did start this post by saying "The TTL rs232 bus is already used on another PCB" my device can be of any specification.
OK, there is an existing PCB with an existing working bus, using one line to TX/RX commands, this bus is "based" on the RS232 protocol in speed and timing only. the devices are connected to this bus using open collector transistors that I know for definite cannot withstand a pull up to 5v of just a few ma and I suspect (yet to check) a few tens on ma down to ground, I have tested the theory of what I want to do by simply placing the wire to +5v supply and GND in both cases all transmissions are blocked and after removing it comms continues without problem.
I want to mimic my manual placing to +5v supply and GND in time with my MCU pin thereby overriding any device talking on the bus and if a device is listening managing to get my command to it, after I issue my command I release the bus and listen for the reply.
Hope this makes things clearer.
P.S. I'll go look at these "data selectors" and thanks for continuing to try and help me
And the funny thing is how most manage to make fools of themselves...Also let me say this. I don't really think the other guy was messing with you. I think he was trying to understand what it is you want, but you are right. There are always a few smart a--s's around. Don't let them get you worked up. I like your attitude. If you say you can do it....then by golly you can! You can do allot of stuff with electronics. There is no such thing as can't. Not in my book and it looks like yours either. So if somebody rubs you the wrong way, just try to ignore it and move on. You got those little nay sayers and hecklers everywhere you go. It's just part of life.