1,000+ ASIC Interview Questions: SystemVerilog, UVM & RTL

DescriptionQ502

Q502DesignASIC interview problem

Increment a four-digit BCD counter

TechniquesBCDReady/validCarry propagation

DifficultyEasy

TopicRTL Design

LanguageSystemVerilog

Requirements4 checkpoints

Problem

Accept four valid binary-coded decimal (BCD) digits, add one without converting the packed value to binary, and return a stallable ready/valid response. Wrap 9999 to 0000 and flag the wrap.

Example input and output

Use this case to check your interpretation

Input

accepted BCD values 1999, then 9999; stall the second response

Output

1999 -> 2000 carry_out=0; 9999 -> 0000 carry_out=1, held stable while stalled

Explanation

Decimal carry propagates across trailing nines, and the all-nine case wraps all four digits with one carry flag.

Requirements (4)

Treat each input digit as a decimal value from 0 through 9.
Propagate decimal carry across any run of trailing nines.
Create exactly one output transaction for every accepted input transaction.
Hold all result digits and carry_out stable while out_valid is asserted and out_ready is low.