Data Structure
Networking
RDBMS
Operating System
Java
MS Excel
iOS
HTML
CSS
Android
Python
C Programming
C++
C#
MongoDB
MySQL
Javascript
PHP
Physics
Chemistry
Biology
Mathematics
English
Economics
Psychology
Social Studies
Fashion Studies
Legal Studies
- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who
Instruction type CMP R in 8085 Microprocessor
In 8085 Instruction set, CMP is a mnemonic that stands for “CoMPareAccumulator” and hereR stands for any of the following registers, or memory location M pointed by HL pair.
R = A, B, C, D, E, H, L, or M
This instruction is used to compare contents of the Accumulator with given register R. The result of compare operation will be stored in the Temp register. Temp is not a GPR (General Purpose Register) but an internal register that is not accessible to the programmer. Actually R register’s content will get subtracted from Accumulators content and difference value will be stored on the Temp register. As R can have any of the eight values, there are eight opcodes for this type of instruction. It occupies only 1-Byte in memory.
| Mnemonics, Operand | Opcode(in HEX) | Bytes |
|---|---|---|
| CMP A | BF | 1 |
| CMP B | B8 | 1 |
| CMP C | B9 | 1 |
| CMP D | BA | 1 |
| CMP E | BB | 1 |
| CMP H | BC | 1 |
| CMP L | BD | 1 |
| CMP M | BD | 1 |
Let us consider one sample instruction CMP E falling in this category.As It is a 1-Byte instruction so during execution of this instruction it will occupy only a single Byte in memory. The result of execution of this instruction has been depicted with following set of examples −
Example 1
| Before | After | |
|---|---|---|
(A) |
50H | 50H |
(E) |
70H | 70H |
(Temp) |
Any value | E0H |
(F) |
Any value | Cy=1,AC=0,S=1,P=0,Z=0 |
Example 2
| Before | After | |
|---|---|---|
(A) |
70H | 70H |
(E) |
50H | 50H |
(Temp) |
Any value | 20H |
(F) |
Any value | Cy=0,AC=0,S=0,P=0,Z=0 |
Example 3
| Before | After | |
|---|---|---|
(A) |
50H | 50H |
(E) |
50H | 50H |
(Temp) |
Any value | 00H |
(F) |
Any value | Cy=0,AC=0,S=0,P=1,Z=1 |
| Address | Hex Codes | Mnemonic | Comment |
|---|---|---|---|
| 2004 | BB | CMP E | Temp = Register A - Register E |
The timing diagram against this instruction CMP E execution is as follows −
Summary − So this instruction CMP E requires 1-Byte, 1-Machine Cycle (Opcode Fetch) and 4 T-States for execution as shown in the timing diagram.
8K+ Views
