$($a$)$ Refer to Fig$($a$)$ for a memory chip, what are the functions of the signal A$0-$A$18,$ D$0-$D$7,$ CS$,$ WE and OE$.$

$($b$)$ Refer to Fig$($b$),$ explain how a particular bit is being accessed by inputting appropriate address A$0-$A$10$ and control signals RAS & CAS.