Q.Briefly explain the different bits of binary memories of different registers.

To program in assembly language you must know each register of the CPU and how many bits of binary data it can hold, since this decides the range of numbers or addresses it can store.

[!ANSWER]

Register A holds 8 bits (1 byte), Register R holds 8 bits of binary data, and Register PC (Program Counter) holds 16 bits (2 bytes) of address.

[!TLDR]

Register A and Register R each store 8 bits (one byte), while the Program Counter (PC) stores 16 bits (two bytes).

To program the 8051 in assembly language, the programmer must know all the registers of the CPU and the size of each, because a register's width fixes the largest number or address it can hold. The three important registers and their binary sizes are:

• Register A (Accumulator) — performs all operations in the CPU and can hold 8 bits, i.e. 1 byte, of binary data. It is where arithmetic and logical results are collected.
• Register R (working registers R0–R7) — stores numbers temporarily and can also hold 8 bits of binary data. These give the CPU short-term storage during a program.
• Register PC (Program Counter) — holds the address of the next instruction to be executed in code memory and can hold a 16-bit (2-byte) address number. A 16-bit counter can address code from 0000H to FFFFH, i.e. the full 64K program-memory space.

Because A and R are 8-bit, the largest value they can hold is FFH (255 decimal); because PC is 16-bit, it can point anywhere in the 64K code memory.

[!ANSWER]

Register A = 8 bits (1 byte); Register R = 8 bits of binary data; Register PC = 16 bits (2 bytes) of address, covering the 64K code-memory range 0000H–FFFFH.