The internal hardware of the HP-12C changed again in 2015, when the design switched to use an Atmel ATSAM4LC2CA-AU processor with ARM Cortex-M4 core. The calculator's part number and physical appearance didn't change except for a "Rev 2" plate on the bottom side. It continues to use two parallel CR2032 cells. The firmware reports a 2015 build date. Serial numbers starting with "PHA", "9CJ", "7CD", or "3CD" rule out the older model variant. The 2×3-pin flash port now uses the USB protocol instead of a TTL serial protocol; in addition to this, the calculator's circuit board features an unpopulated mount for a Micro-USB connector.