On Mon, Jan 22, 2018 at 12:54 AM, Jeffrey Jonas via vcf-midatlantic <vcf-midatlantic@lists.vintagecomputerfederation.org> wrote:
Once modems gained DSP (digital signal processors), the data format you "fed it" externally bore little relationship to the symbols used among the modems.
It's worth noting that there was a third generation of modems where they actually removed the DSP and did everything entirely in software (to reduce cost). These "winmodems" did all the signal processing on the host CPU (including error correction) and then the modem hardware itself was just a simple D/A. These were the norm in the mid to late 1990's unless you bought a more expensive modem such as the US Robotics Sportster.
External modems usually use asynchronous serial via RS232 to a UART. Internal modems are parallel, so there's no stop/start bits.
This is generally true, although many internal modems actually had an onboard 8250/16550 UART. Hence from a software/application perspective, they were indistinguishable from external modems. Devin -- Devin J. Heitmueller http://www.devinheitmueller.com