A block diagram of an Si2400 modem chip, and a Si3015 line-side companion chip, with a capacitor linking the two.

Notices where this attachment appears

1. Embed this notice
   abrasive (abrasive@digipres.club)'s status on Monday, 08-Sep-2025 04:12:51 JST abrasive

   in reply to

   Another dated bit is hiding under the plastic cover - a modem! The Australian PSTN is supposed to be retired this year but in most residential areas it's been gone for years.

   This modem chipset is kind of cool, it's a Si2400 "ISOmodem". The idea is that this replaces the traditional big expensive isolation transformer with a pair of high-voltage capacitors, providing an isolated data (and possibly power) link to a second chip on the line side which handles the analog business. Neat!