ECI : All the three units, CU, BU, VVPAT, have... ... Plea For 100% EVM-VVPAT Verification : Supreme Court Seeks Clarifications From ECI | LIVE UPDATES

ECI : All the three units, CU, BU, VVPAT, have their own microcontrollers. These microcontrolers are housed in it. They cannot be accessed physically. The one-time program is burnt into them.

ECI : All the microcontrollers are one time programmable. They are burnt at the time of manufacturing. They cannot be changed.