MC9S12G Datasheet, PDF (331/1160 Pages) Freescale Semiconductor, Inc – Ignores external trigger. Performs one conversion sequence and stops.

S12 Clock, Reset and Power Management Unit (S12CPMU)
The COP will continue to run on ACLK.
The clock configuration bits PLLSEL, COPOSCSEL0, RTIOSCSEL are unchanged.
NOTE
When starting up the external oscillator (either by programming OSCE bit
to 1 or on exit from Full Stop Mode with OSCE bit already 1) the software
must wait for a minimum time equivalent to the startup-time of the external
oscillator t_UPOSC before entering Pseudo Stop Mode.
MC9S12G Family Reference Manual, Rev.1.01
Freescale Semiconductor
331
This document is valid for the S12G96 and the S12G128 device. All information related to other devices is preliminary.