A circuit module contains a sub-circuit that is capable of providing a
level of performance dependent on the version number that is stored in a
version number memory. The version number is passed to the sub-circuit
from a write-protected memory to the version memory in the multiplex mode
with normal operating signals for the sub-circuit. In one embodiment
various commands for the circuit module are received from outside the
circuit module and distributed in the circuit module via a communication
bus. A watchdog monitors received commands for an update command that
commands updating of the version number in the version number memory and
if so it passes said update command to the communication bus, replacing a
version number in the update command by a version number from the
write-protected memory. In another embodiment the version number is
passed to the sub-circuit in time-slot multiplexing with the signals that
are processed, for example in a blanking period of a video signal that is
being processed.