which illustrates four explicit routines of the microcomputer 97 which are effected in cooperation with the switches sw d sw b sw f sw l sw c and sw m to control operation of the motorized film drive mechanism 83 this mode corresponds to the routine l of the microcomputer 97 if the switch sw d is closed because the rear door 7 is closed the switch sw b is closed because the shutter release button 39 is depressed and either a the switch sw l is open because the lens cover 1 is open and the switch sw f is open because no film is present on the take up spool 1 or b the switch sw l is closed because the lens cover is closed the switch sw f is open and the switch sw c is closed because the cartridge c is in the loading chamber 17 then a shutter solenoid 115 will be actuated to release the camera shutter not shown for opening and closing following this the motor 85 will be energized to drive the transmission 87 in a pre wind direction for film movement as depicted by the arrow r in fig6 the transmission 87 will rotate the metering sprocket 43 and the drive hub 89 for the take up spool 33 at this time the drive hub 91 for the supply spool 11 of the cartridge c is disconnected from the transmission 87 allowing the supply spool to idle after the motor 85 is energized the up down counter 109 will begin to count up from 34 0 34 by 34 1 34 each time a metering pulse is produced in response to closing of the switch sw m when the metering sprocket 43 completes a single revolution if.