Polish stepper motor Microma

Stepper motor: Microma FB 20-4-1A, 15 deg., 0.2 Nm, 28V, insulation class B, manufacturing date VI/88. Connection: unipolar, BLACK -- common, RED and YELLOW -- 1st phase, BROWN and WHITE -- 2nd phase, 2 GREEN wires -- I don’t know what is it... Driver: ULN2003AN. MCU: MSP430G2553. I haven’t 28V power supply, I used 12V instead. Motor is warm, but driver is very HOT :)