Question based on concept of 8085 instructions length and special purpose registers

Lesson 6 of 10 • 1 upvotes • 12:05mins

Akhilesh Pandey

General Purpose Register There are six 8-bit general purpose registers: B, C, D, E, H, L There are three 16-bit general purpose register pairs: BC, DE, HL HL register pair is default memory pointer, i.e. memory M is stored in the address represented by HL pair. Accumulator: it is an 8-bit re Special Purpose Register Program counter (PC): It is 16-bit register which contains the address of next instruction to be executed. Stack Pointer (SP): It is a 16-bit register which contain address of data present at the top of stack or it points to the data present at the top of stack. Stack is a part of read/write memory which is used to store temporary data. When data is stored or push into stack memory, stack pointer is decremented. When data is accessed from stack memory, stack pointer is incremented. Op-code and Operand Op-code: It indicates the type of operation to be performed for an instruction Operand: It is a data on which operation is to be performed. Operand can be a register, memory location, register pair, 8-bit data address, or 16-bit data address. Mnemonic code: In 8085, we use mnemonic codes to write programs Length of Microprocessor Instruction It is the number of bytes that an instruction occupies in the memory. For each mnemonic 1 byte Hex code is defined and remaining length is due to data. There are 3 types of instruction on basis of its length 1-byte instruction MOV A, C : 1 byte Hex code for mnemonic MOV A, C 2-byte instruction: MVI B, 77 H : 1 byte Hex code for mnemonic MVI B + 1 byte for data 3-byte instruction: LXI H, 9080 H : 1 byte Hex code for mnemonic LXI H + 2 byte for data