ERJ 190 EICAS INDICATED A FAILURE OF THE AVIONICS UNIT; WHICH DICTATES A LNDG AT THE NEAREST SUITABLE ARPT. EMER WAS DECLARED AND AN UNEVENTFUL LNDG WAS ACCOMPLISHED.

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WHILE CLBING TO OUR ASSIGNED ALT OF FL260; WE RECEIVED AN 'AVNX MAU 3A FAIL' EICAS MESSAGE (AND OTHER ASSOCIATED EICAS MESSAGES). WE HAD 86 PAX ON BOARD. WE FOLLOWED THE AVNX MAU 3A FAIL QRH PROC WHICH REQUIRES A LNDG AT THE NEAREST SUITABLE ARPT. GIVEN OUR POS; WE DETERMINED THAT ZZZ WAS THE NEAREST SUITABLE ARPT. WE RECEIVED A CLRNC BACK TO ZZZ FROM CTR; DECLARED AN EMER; NOTIFIED THE FLT ATTENDANTS; PAX AND OPS (WHO WE ALSO HAD NOTIFY OUR DISPATCHER). WE HAD THE EMER EQUIP STANDING BY FOR OUR LNDG ON RWY XXL. THE LNDG AND ROLLOUT WERE UNEVENTFUL. WE TAXIED UNDER OUR OWN PWR TO THE GATE. AT THE GATE; I CALLED OUR DISPATCHER ON THE PHONE. THE FO DID AN OUTSTANDING JOB THROUGHOUT THIS EVENT AND MADE MY JOB MUCH EASIER. I COMMEND ALL WITHIN OUR COMPANY RESPONSIBLE FOR HIRING AND TRAINING OUR NEW PLTS -- ALL THE FO'S I HAVE FLOWN WITH DO A GREAT JOB! MAINT THOUGHT IT WAS A FAILURE OF A CIRCUIT CARD IN THE 3A MODULAR AVIONICS UNIT. WHEN WE LEFT THE ACFT; A FINAL DETERMINATION HAD NOT BEEN MADE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE REPORTER INDICATED THE MODULAR AVIONICS UNIT HAD FAILED. THIS RESULTS IN FAILURE OF THE AUTOPILOT; AUTOTHROTTLE; AND FLT DIRECTOR. UNITS THAT MAY SUBSEQUENTLY BE AFFECTED INCLUDE SOME FAILURE OF SPOILERS AND REDUCED BRAKING CAPABILITIES.