This repository contains a reverse engineered schematic for the 6499, a modem made by Celint for Commodore in Italy.
It was able to connect the Commodore 64 with Sip Videotel/prestel in V.23 1200/75 and compatible V.21 300/300 on BBSs in scroll mode.
inside the 27c256 there is the software necessary for the connection that starts automatically when the c64 is switched on with the cartridge inserted.
note: Sip is the name of old Telephone company in Italy now TIM
you can see 6499 modem in action here https://www.youtube.com/watch?v=_4FbsT731f0
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