MICROPROCESSOR AND MICROCONTROLLER

Detailed explanation-1: -CX is the “count” register. The looping instructions (LOOP, LOOPE, and LOOPNE), the shift and rotate instructions (RCL, RCR, ROL, ROR, SHL, SHR, and SAR), and the string instructions (with the prefixes REP, REPE, and REPNE) all use the count register to determine how many times they will repeat.

Detailed explanation-2: -CX is known as the count register, as the ECX, CX registers store the loop count in iterative operations. DX is known as the data register. It is also used in input/output operations. It is also used with AX register along with DX for multiply and divide operations involving large values.

Detailed explanation-3: -The LOOP instruction is mainly used to simulate the different loops in HLL. The Loop instructions use the CX register to indicate the loop count. Note that the ECX register can be used as a loop counter in 32-bit mode.

Detailed explanation-4: -REP − Used to repeat the given instruction till CX ≠ 0. REPE/REPZ − Used to repeat the given instruction until CX = 0 or zero flag ZF = 1.

Detailed explanation-5: -CX is used as a default counter in case of string and loop instructions. The loop instruction is executed based on the value in the CX register.