Page 53 - DCAP210_INTRODUCTION__TO_MICROPROCESSORS

Unit 3: Assembly Language Programming of 8085

For example: Notes

Task Opcode Operand Binary Code Hex Code
Transfer the JMP 2085H 1100 0011 C3 First byte
program sequence 100001010 85 Second byte
to the memory 010 0000 20 Third byte
location 2085H.

This instruction would require three memory locations to store in memory.
Three-byte instructions — opcode + data byte + data byte
LXI rp, data16
rp is one of the pairs of registers BC, DE, HL used as 16-bit registers. The two data
bytes are 16-bit data in L H order of significance.
rp <— data16

Example: LXI H,0520H coded as 21H 20H 50H in three bytes. This is also immediate

addressing.
LDA addr
A <— (addr) Addr is a 16-bit address in L H order. Example: LDA 2134H coded as 3AH 34H 21H.
This is also an example of direct addressing.
3.4.5 Opcode Format
In the design of the 8085 microprocessor chip, all operations, registers and status flags are identified
with a specific code. First understand how an instruction is designed into the microprocessor,
which will be useful in reading a user’s manual. In user manual, the operation codes are specified
in binary format and 8-bits are divided into various groups. All internal registers are identified
as follows:

Table 3.7: Internal Registers and Their Codes

Code Register pairs

00 BC
01 DE
10 HL
11 AF or SP

Code Registers
000 B
001 C
010 D
011 E
100 H
101 L
111 A
110 Reserved for memory related operation

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