Garmin Cirrus Perspective SR20 Pilot's Manual page 17

• GDC 74A (1 or 2) – The Air Data Computer (ADC) processes data from the pitot/static system and outside air
temperature (OAT) sensor. This unit provides pressure altitude, airspeed, vertical speed and OAT information
to the system, and it communicates with the primary GIA 63W, GDU 1240A and GRS 77, using an ARINC 429
digital interface (it also interfaces directly with the primary GTP 59).
• GEA 71 (1) – Receives and processes signals from the engine and airframe sensors. This unit communicates
with both GIA 63Ws using an RS-485 digital interface.
• GRS 77 (1 or 2) – The Attitude and Heading Reference System (AHRS) provides aircraft attitude and heading
information via ARINC 429 to both GDUs and the primary GIA 63W. The GRS 77 contains advanced sensors
(including accelerometers and rate sensors) and interfaces with the primary GMU 44 to obtain magnetic field
information, with the GDC 74A to obtain air data, and with both GIA 63Ws to obtain GPS information. AHRS
modes of operation are discussed later in this document.
• GMU 44 (1 or 2) – The Magnetometer measures local magnetic field and sends the data to the GRS 77 for
processing to determine aircraft magnetic heading. This unit receives power directly from the GRS 77 and
communicates with the GRS 77, using an RS-485 digital interface.
190-00820-08 Rev. A Cirrus Perspective by Garmin – Pilot's Guide for the SR20/SR22/SR22T
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SYSTEM OVERVIEW
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