(c)  
A brief press of the CLR key will erase the last character entered in the scratchpad. A longer press of the CLR key will erase the entire scratchpad entry.

 (d)  
Pressing the DEL key will enter the word DELETE into the scratchpad field, pressing one of the twelve line select keys will delete the data in the selected field.

 (e)  
The SP key will enter a space into the scratchpad field.

 C. Operational Description
 (1)  Data Entry
 (a)  
Alphanumeric entries are entered into the scratchpad. This entry is then transferred to the field selected by a line select key (LSK) next to the desired field. A valid entry will clear the scratchpad after the LSK has been selected. An invalid entry will be followed by an advisory message appearing in the scratchpad. The entered data will be retained and can be retrieved by pressing the CLR key.

 (b)  
It is also possible to transfer data into the scratchpad using the LSKs. This is accomplished by pressing the particular LSK while the scratchpad is empty. The data is transferred into the scratchpad and can then be transferred to the desired field by pressing the adjacent LSK.

 NOTE:____Not all fields are capable of data transfer. For example the OP PROGRAM field on the IDENT page.
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 (c)  Another form of data entry is automatic data entry. This is done, for example, when initalization data is to be entered. The FMC gathers the desired data from either the navigation data base or the performance data base and automatically enters this data into its respective fields within the pages of the CDU.
 D. FMC Failure Page Display Characteristics.
 (1)  
If an FMC fails while the airplane is on the ground the onside CDU will display the MENU page without the <FMC prompt. The offside CDU will continue displaying the selected pages.

 (2)  
If the master FMC (indicated by the master switch) fails while the airplane is in the air, both CDUs will display the MENU page without the <FMC prompt. Selection of the operational FMC, on the FMC master switch, is required to enable the operator to select the <FMC prompt on the CDU for FMC control.

 E. CDU Interfaces
 (1)  
Central Maintenance Computer (CMC) (Fig. 24 and 25)

 (a)  
The MENU page displayed on the CDU provides access for CMC control. Pressing the LSK next to the <CMC prompt will display the CMC MENU page. This page allows for CMC testing of selected LRUs. The CMC will log all fault messages pertaining to the confidence test initiated by the CMC. The CDU will also display these faults.

 (b)  
The CDUs will be inhibited from CMC interaction when the airplane is greater than 80 knots during takeoff and less than 10,000 feet AGL.

 (c)  
The CDU will receive a subsystem identifier and text transfer signal from the CMC. The CDU will supply keyboard selection, CDU BITE data and the CDU identifier. This transfer of data will be low speed ARINC 739 bus format.

 (2)  
VHF NAV radio interfaces (Fig. 24 and 25)

 (a)  
The CDU directly interfaces with the VOR, DME, ADF and ILS receivers. These direct interfaces allow for manual tuning of VHF NAV radios, as well as an alternate method for VHF NAV radio tuning in the event both FMCs fail.

 (b)  
Frequencies or navaid identifiers can be entered into the CDU NAV RADIO page for manual tuning of VHF NAV radios. Both left and right VHF receivers can be manually tuned from a single CDU when on the NAV RADIO page. In case of the master FMC failing the right CDU will tune the right VHF NAV radio, center CDU the center VHF NAV radio (ILS), and the left CDU the left VHF NAV radio.

 (c)  
The data transfer from the CDU will be ADF, DME, ILS and VOR frequencies . This data is transmitted over a low speed ARINC 429 data bus.

 (3)  
EFIS Control Panel(Fig. 24)

 (a)  If the EFIS CP is operational, all of it's information as well as the EICAS CP information is sent through the CDU to the EIUs, WX RADARs, FMCs and the ADCs.
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