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 B.  The CU converts 115 volt ac power to regulated dc power and then generates accurately timed pulses and square waves for timing control. All input signals to the CU are converted to pulses representing ones and zeros in the binary numbering system. All operations performed in the central processor and information stored in memory are in the binary form.
 C.  The read only memory card is used to store permanent data while the magnetic memory is used to store both permanent and temporary data. Constants required for computations, comparisons and limitations are stored permanently. The computer program, which consists of instruction words, is also permanently stored in memory. Once the computer program is initialized at turn on, the programmed instructions control the computer operation. The magnetic memory is used for program storage and storage of data from computations or from the input/output section of the computer.
 D.  The central processor is the data processing center of the CU. The processor contains logic circuits which perform the operations on data in the CU. These operations include decoding the instructions received from the memory, selecting the next instruction or data to be obtained from the memory or the input/output, keeping track of the next sequential instruction (part of each instruction word) modifying a sequence of operations based on computational results or on inputs, and performing the operations commanded by the instructions.
 E.  The digital input/output cards receive digital data inputs and provide digital data outputs in either binary or BCD form. The analog input/output cards convert synchro, analog and discrete inputs to binary data and binary data outputs to analog and discrete outputs. The analog output signals are reconverted to binary data for comparison in the CU. The reconverted data is checked against the data used to generate the analog signals to ensure that conversions are correct.
 10. Engine Interface Unit (Fig. 1)
_____________________
 A.  The engine interface unit (EIU) contains two circuit cards, which contain multistage binary counters that format binary serial data for use by the computer unit.
 B.  The EIU receives fuel flow signals for each engine, N1 (RPM) signals for each engine and discrete signals from other airplane systems. These signals include discretes for engine bleed air, anti-ice, air conditioning and flap position. The input data is converted to binary serial data that is transmitted to the computer unit.
 11. Switching Unit (Fig. 1)
______________
 A.  The basic function of the switching unit (SU) is to switch the throttle servomotor from the auto throttle system (ATS) to the performance management system (PMS), when the PMS mode of operation is selected.
 B.  The PMS computer unit provides thrust commands to a servo amplifier in the PMS switching unit. In the PMS mode of operation the servo amplifier uses these commands to control the throttle servomotor. When a mode of operation other than PMS is selected the switching unit switches the throttle servomotor back to the auto throttle system.
 C.  The switching unit contains power supplies, relays, logic circuits, lamp drivers, transformers and a servo amplifier.
 12. Descent Mode Annunciation (Fig. 1)
_________________________
 EFFECTIVITY
 AIRPLANES WITH PMS    01 Page 27  Aug 25/83

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 A. PATH ARM Annunciator

 (1)  The path arm (PATH ARM) annunciator lights amber when:
 (a)  
The descent path mode is manually armed during cruise.

 (b)  
The PMS is in the descent path mode or in the descent flight path angle (FPA) mode, and Vmin/Vmax limits are reached.

 NOTE: If Vmin/Vmax limits are reached during a path descent,
____ the path arm annunciator lights to indicate that in the path mode, speed control is given priority over path control. In this condition the SPEED annunciator will also light.
 (2)  The path arm annunciator will flash during cruise if the descent path mode is armed, the airplane is within 15 nautical miles of top of descent (TOD), and a clearance altitude is not selected below present cruise altitude. The annunciator will light steadily when the clearance altitude is set below cruise altitude.
 B. PATH Annunciator
 (1)  The Path (PATH) annunciator lights green when the PMS is controlling to a geographically defined descent path, in the descent path mode or in the descent flight path angle (FPA) mode, within Vmin/Vmax limits.
 C. SPEED ARM Annunciator
 (1)  
The speed arm (SPEED ARM) annunciator lights amber when:

 (a)  
The descent speed mode is manually armed during cruise.
　
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