AM7910 AM7911

[neazoi]

Hello,
I would like to experiment with this chip for making a small modem. I see that it does provide the pins for RS-232, but some designs use external transceiver chips, so I am a bit confused.
Is this chip RS-232 ready or does it need external converters (MAX232)?
Thanks

 

[betwixt]

TTL levels I'm afraid, you still need a converter if you need RS232. They are old obsolete devices!

Brian.

 

[neazoi]

TTL levels I'm afraid, you still need a converter if you need RS232. They are old obsolete devices!

Brian.

I am trying to find modem chips in through hole package (or at least PLCC, which can be converted to through hole with sockets), that support both bell103 (used on HF) and bell202 (used on VHF), so that to make a kind of universal modem for inter-connectivity of all these networks, including land-lines, GSM etc.

Problem is as always code skills so I do not want to mess with MCUs, but just plain jumpers etc.
If you have any such modem IC in mind, or any other ideas, it would be greatly appreciated.

Thanks Brian

 

[betwixt]

Both those modulation schemes are very old and not used commercially these days so it is very unlikely any modern devices will support them.
You could try using PLL lock detection with devices like the NE556 to recover the data by seeing if one of the frequencies was in the lock range then using the lock detect output or you could try with a CMOS CD4046 and select a different VCO frequency for Bell 103 or 202.
Producing the tones can be done by simply switching VCO frequency with the data. It would be wise to add an LPF at the output in case switching shortened any output frequency cycles and made higher frequencies appear.

Brian.

 

[neazoi]

Both those modulation schemes are very old and not used commercially these days so it is very unlikely any modern devices will support them.
You could try using PLL lock detection with devices like the NE556 to recover the data by seeing if one of the frequencies was in the lock range then using the lock detect output or you could try with a CMOS CD4046 and select a different VCO frequency for Bell 103 or 202.
Producing the tones can be done by simply switching VCO frequency with the data. It would be wise to add an LPF at the output in case switching shortened any output frequency cycles and made higher frequencies appear.

Brian.

I remember that in UK you use 4-lines on landlines, a pair for TX and a pair for RX. What is the pinout of this RJ plug? Also what happens if one connects a 2-wire modem to this 4-line you use in UK?
Thanks

 

[betwixt]

Four wires are connected but only two carry the voice/data, the others are the bell line (aka 'the anti-tinkle line') used to stop bells on parallel phones ringing when one is pulse dialling out and the loop recall line used to signal back to the switchboard (if there is one). Only two active wires arrive at the premises with two kept as spares or for a second line, the bell and loop lines are only run internally.

Usually, only the two center pins are used on the RJ11 plug.

Brian.

 

[neazoi]

Four wires are connected but only two carry the voice/data, the others are the bell line (aka 'the anti-tinkle line') used to stop bells on parallel phones ringing when one is pulse dialling out and the loop recall line used to signal back to the switchboard (if there is one). Only two active wires arrive at the premises with two kept as spares or for a second line, the bell and loop lines are only run internally.

Usually, only the two center pins are used on the RJ11 plug.

Brian.

All right, the two center lines. In Greece we also use the two center lines (only 2 lines total here). So modems from one country should be compatible with modems from the other. At least when considering simple FSK passed through the line, ignoring the other signals you referred to. Great news!

 

[FvM]

Analog telephone systems use two wire line and hybrids in the terminal devices since the very beginning. Long distance connection uses analog carrier frequency or digital transmission and thus translation to "four wire" the latest at the telephone switch, these days already in your VoIP modem.

A modem like AM7910 also needs a hybrid to connect to the telephone line, the datasheet shows an example.