Editing Psion Organiser II (section)

=== Real-time clock and the 34-minute wake-up ===

The control IC contains a '''27-bit divider chain''' split into two stages. Stage 1 is a 15-bit counter clocked at 32768 Hz, so its top bit runs at 1 Hz. Stage 2 is a 12-bit counter.<ref name="tech2" />

While the machine is on, the 1 Hz signal goes to the processor's NMI input and the clock is updated every second. When the machine is switched off, the 1 Hz signal is instead routed to stage 2, and when stage 2 times out — after '''34 minutes and 8 seconds''' — it '''switches the Organiser on by itself''', lets the processor add 34 min 8 s to its time registers, and switches off again.<ref name="tech2" />

That is why an Organiser left switched off still keeps good time, and it is also why a machine sitting in a drawer draws a little more power than a pure standby figure would suggest.