FMCS Digital Outputs Figure 7 (Sheet 2)
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 (4)  Input/Output Processor
 (a)  
The Input/Output (I/O) processor performs functions associated with I/O handling. The I/O processor is implemented by a microprocessor. The microprocessor functions in a manner equivalent to the CPUs in the navigation and performance processors. However, the microprocessor does not employ floating point arithmetic.

 (b)  
The digital interface circuits provided in the FMC are of the type characterized by ARINC 429 Digital Information Transfer System (DITS). The ARINC Input/Output (I/O) circuits provide up to 6 high-speed and 26 low-speed input receivers. The ARINC I/O circuits also provide 6 high-speed and 4 low-speed output transmitters. These ARINC interface circuits are managed by a dedicated ARINC controller. The controller is in turn controlled by an I/O processor. The controller processes all input words on all channels, and passes on to the I/O processor only the required parameters. All other word labels are ignored. This provides for fast response to changes in inputs directly affecting the FMCS's computations. The controller also activates and maintains all output channels.

 F. Memory
 (1)  
The FMC storage is made up of three types of memory: Erasable Programmable Read-Only Memory (EPROM), Nonvolatile Random Access Memory (NV RAM), and High-Speed volatile Random Access Memory (HS RAM). The EPROM contains both program instruction and fixed data, while the RAMs contain the navigation data base and are also used for scratch pad.

 (2)  
Power for the NV RAM memory is provided by the computer power supply whenever power is applied to the FMC. When power is removed, the memory elements are switched to a low-power standby state for data retention. Power for the standby mode is provided by an internal solid-state dry lithium battery. The battery provides nonvolatile data storage with the RAM memory.

 G. Navigation Data Base
 (1)  The FMCS navigation data base is stored in the NV RAM memory of the FMC, in two parts. One part contains active permanent data, which is effective until a specified expiration date; the other part contains a set of data revisions for the next period of effectivity. These effectivity dates can be displayed on the CDU. The set of data for the current period of effectivity is selected as the active navigation data base, in order to enable the navigation and guidance functions.
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737-300/400/500MAINTENANCE MANUAL
 (2)  
The navigation data base contains all information required for operation in a specified geographic area. This information includes data for:

 (a)  
VOR, DME, VORTAC, and TACAN navigation aids

 (b)  
Waypoints

 (c)  
Airports and runways

 (d)  
Terminal area procedures and approaches.

 (e)  
Enroute airways

 (f)  
Holding patterns

 (g)  
Company route structures

 (3)  
As a supplement to the content of the permanent current navigation data base (and data base revisions); the system will accept operator-entered data for additional navigation aids, waypoints, and airports. These entries will be retained in the FMC memory until modified or deleted by the operator.

 (4)  
Data Base Update Loading

 (a)  
Upon the expiration date of the navigation database, a new navigation database should be loaded into the FMC. The new database must be valid for the next period of effectivity.

 (b)  
When the airplane is on the ground, an external portable data loader can be connected to a flight deck mounted electrical receptacle. Connecting the loader to the receptacle allows the loader to load and update the navigation data base, without removing the FMC from the airplane.
　
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