General operations:
1) both trunks follow the same HV serial programming specification in the datasheet; Different fuse values are used to for different chips, based on the detected target device signature.
2) The 16x2 lcd version simply writes to the lcd and follows a linear process; The 7-segment led version utilizes timer0 interrupt (in this particularly case, the chip runs at 1Mhz Fcy and the timer0 prescaler is set to 8:1, so each digit is shown for 8*256us = 2ms). In the isr, individual digits are updated from a display buffer (of 4 bytes, containing the font information for each digit). The isr runs in the background and the user only needs to update the display buffer when new information needs to be sent to the 7-segment display, the isr handles the rest.