y = a bitand b
a bitand b performs a bitwise AND between a and b. Both a and b are treated as 32-bit (4-byte) integer values, so an eventual fraction will be ignored.
In 20-sim, all bitwise function arguments are treated as 32-bit integers. Thus the binary representation of 30 (ignoring leading zeroes) is equal to 11110 as shown in the figure below. Similarly, the binary representation of 9 is 1001. The binary value of 30 bitand 9 is equal to 01000, which corresponds with decimal value of 8.
a and b must be integers.