The 4100-1210 Analog Audio Controller, 4100-1211 Digital Audio Controller, 4100-1311 Digital Audio Controller, and their respective option cards make up the audio controller subsystem of the Fire Alarm System. The controller is the head end of the audio system, and is seen by the system CPU as a single slave: only the audio card is visible, while any option cards appear logically as memory-mapped locations on the audio controller. The main function of the audio controller card is to control system audio inputs and to recreate stored audio messages for distribution throughout the system. Analog audio inputs to the system include local and remote microphones and fire fighter phone option cards, and can be expanded through the use of the 4100-1240 Audio Input Option Card. Pre-recorded messages are stored on the audio controller’s FLASH memory and can be expanded through the use of the 4100- 1241/1242 Message Expansion Card.