Garmin GPS 155 Repair Manual
Also see for GPS 155: Pilot's guide addendum
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Contents
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The block diagram in Figure 2 shows the interaction between components on the Control/Display Unit.Figure 2Control/Display Unit Block Diagram1.2.2 Main Board AssemblyThe Main Board Assembly contains the CPU, operating system ROM, system memory, discrete I/O, ser-ial communication drivers/receivers and the power supply. These items are discussed in further detailbelow.1.2.2.1 Central Processing Unit (CPU)The Main Board is a microprocessor-based computer board. This board contains an Intel 80L186EBmicroprocessor running at 16 MHz, a plug-in read only memory chip (ROM) and random access mem-ory chips (RAM). Data stored in RAM is maintained by a 3 volt lithium battery when the unit isswitched off, and by the regulated 5 volt supply when the unit is powered on. A custom LSI is used todecode the signals from the GPS satellites. A real time clock IC is used to keep track of the date andtime. Other circuits on the board are used for input/output functions such as controlling the display,reading the keypad, and controlling the receiver. Discrete input/output lines are provided for CDIcourse deviation, CDI to/from flag, CDI NAV flag, Super Flag, external annunciators, OBS course, andto activate the Approach mode. Serial communication lines for OBI (clock/data/sync), ARINC 429, RS-422 and RS-232 (two channels) are also included.3 |
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