alt Hacker NewsI don't understand why a modem would need additional hardware to do its own dialing. Why couldn't the software just send the dialing pulses/tones?
Is it something to do with a difference in voltage between dialing noises and regular calling noise?
I don't understand why a modem would need additional hardware to do its own dialing. Why couldn't the software just send the dialing pulses/tones?
Is it something to do with a difference in voltage between dialing noises and regular calling noise?
Pulse dialing is not sound (although you certainly can hear it), it's the phone circuit closing and opening. This modem plugs into a modular handset connector for a phone, that's after the hook switch and the duplex, so it's got two lines for microphone and two for speaker, and it can't hang up the line, so it can't pulse dial.
It could potentially do tone dialing, but that does need more hardware. A modern telephone modem is basically 8-bit 8000Hz PCM and DSP algorithms, but an 300 baud modem uses 4 fixed frequencies (from wikipedia):
> The originating station used a mark tone of 1,270 Hz and a space tone of 1,070 Hz.
> The answering station used a mark tone of 2,225 Hz and a space tone of 2,025 Hz.
DTMF dialing needs 7 different frequencies and you have to generate two frequencies at once. You might also want to detect dialtone which fully standardized in the 80s and anyway is a different set of frequencies.
Even if you had tone dialing, a lot of people had lines without tone dialing in the 80s, so it's going to be a fringe feature ... and if you already have to manually pick up the phone, because the modem lacks a hook switch and a duplex, might as well also dial the phone manually too.