74HC943 output tone when no data TX?

[neazoi]

Hi,
On this chip, I do not understand how to connect the CDA pin.
The applications of the chip, show a 100nF capacitor connected to the ground.

But the description text on the datahseet, refers to a variable voltage.

Should I somehow connect the wiper of a voltage divider potentiometer to this pin, so I can set the threshold?

Some help is appreciated.

 

[d123]

Hi,

I'm guessing 'no' to the trimpot question. Page 8 of the NXP datasheet goes into a little more detail. All the schematics in both datasheets show a 0.1uF capacitor to ground and that is also what is suggested in that document if the internal 1.2V reference is used. Page 9 shows a bit better, not much but a little more detailed, what is on the other side/inside of the CDA pin.

 

[neazoi]

Hi, I have this 74HC943 modem IC and I want to determine, if there will be any tone presented on it's TXA pin, when there is no data transmitted

I am interested to find this out in both, originate and answer modes setting (pin 13).

I am confused a bit on how this bell103 works, does it present a tone in the channel even when no data is transmitted or it keeps the channel silent?

HAM radio software (RTTY), seems to transmit a sequence of a character, just to keep the channel open when there is no data sent.

 

[FvM]

When transmission is idle, the modem sends continously the space (sorry, actually mark) tone, unless you activate transmitter squelch.

 

[neazoi]

When transmission is idle, the modem sends continously the space tone, unless you activate transmitter squelch.

Are you sure FvM? You talk about the bell103?
I just found that this character is the rtls, at least in ham radio https://www.aa5au.com/rtty/diddles-by-w7ay/
I am not sure that RTTY complies with the bell103 though.

UPDATE
I am sorry I have asked for this chip, not in general for RTTY, I just realized that.
So there is a tone sent when TX is idle, this is clear.

 

[FvM]

Right, I'm talking about the modem. It can be used for different transmission protocols, some may send idle or synchronization characters. Standard UART however doesn't, it keeps TxD at high level or "mark" in idle state.