CrazyEngineers Archive
Old, but evergreen and popular discussions on CrazyEngineers, presented to you in read-only mode.
@Shailaja Tiwari • 18 Jan, 2013 • 1 like
HI,
ashwin sarangula
wow. .. great job biggie.......cheers for CE.
may this number be doubled month by month
well,i would like to share your words.
since you are somewhat from my discipline i would rather like to ask you question .
"what is the difference between 1-byte instruction ,2-byte instruction and 3-byte instruction?" .this question might sound somewhat easy but i am experiencing difficulty in understanding it.i hope you would help me and sorry for such a big story.
@ashwin sarangula • 19 Jan, 2013
shailaja revathi
HI,
well,i would like to share your words.
since you are somewhat from my discipline i would rather like to ask you question .
"what is the difference between 1-byte instruction ,2-byte instruction and 3-byte instruction?" .this question might sound somewhat easy but i am experiencing difficulty in understanding it.i hope you would help me and sorry for such a big story.
hi shailaja, i would be glad to know whether you were talking about the opcodes ?
@Shailaja Tiwari • 19 Jan, 2013
ashwin sarangula
hi shailaja, i would be glad to know whether you were talking about the opcodes ?
yes i am talking about the opcodes.
@ashwin sarangula • 19 Jan, 2013 hey first tell me what do you
shailaja revathi
yes i am talking about the opcodes.
hi shailaja, as you are asking this question , i hope you know some thing about opcodes. i will try to give answer to your question as per my knowledge.
well , coming to the point, as we know that all the instructions are converted into the binary format right.now, for example,if we consider an hexadecimal number,it occupies 8 bits or 1 byte of space, if we have a combination of more number of such numbers, then the combine size of the instruction converted to binary code with be mutipled.
this is just an example the same can be applied all types of microinstructions.
thats what i feel from my perspective. even iam learning this presently, in my course, i would also like to know more about this..........
@Shailaja Tiwari • 19 Jan, 2013 • 1 like ok thanks. but why is it that in one byte instruction both the opcodes and operands are in the same byte and why is the case different with three byte and two byte instruction?someone said that in 1 byte the operand is present within the instruction itself/the register used for data transfer or other operation ,though i am not satisfied with her answer . i am still confused.need to know more about this.
@rahul69 • 20 Jan, 2013
shailaja revathi
ok thanks. but why is it that in one byte instruction both the opcodes and operands are in the same byte and why is the case different with three byte and two byte instruction?someone said that in 1 byte the operand is present within the instruction itself/the register used for data transfer or other operation ,though i am not satisfied with her answer . i am still confused.need to know more about this.
Guess u r confused, but it is alright as it is a little tricky concept, also I am no expert so feel free to correct me . So lets see it thoroughly 😀.
An instruction consist of two main parts : Opcode and operands, so the three troubling cases:
One byte instruction: In this instruction, both opcode and operands are stored in single byte.(now u may ask why?), because opcodes in this category are simple (eg MOV,ADD etc.) and take less space than a single byte and operands are internal registers,and hence can be directly coded into instruction.
Two byte instruction: Here the opcode occupy one byte. The operand occupy one byte too.
Three byte instruction: Here opcode occupy one byte and operand two bytes. In this case operand is bigger and hence cannot be accommodated in single byte.
Hope it clears ur doubt,😀. Feel free to ask if u face difficulty 👍
@Shailaja Tiwari • 24 Jan, 2013 why does the exchange operation take place between the DE and HL pair only?why is BC pair not involved?
please do help.
@rahul69 • 24 Jan, 2013
shailaja revathi
why does the exchange operation take place between the DE and HL pair only?why is BC pair not involved?
please do help.
I think it is because, they are made that way. BC is used by instructions as a Byte Counter.
@Shailaja Tiwari • 24 Jan, 2013 Could you please eloborate this point of yours as it has'nt solved my doubt.😨
@rahul69 • 25 Jan, 2013
shailaja revathi
Could you please eloborate this point of yours as it has'nt solved my doubt.😨
My answer was "they are made that way". which means that since BC was used as byte counter, so the people who made Assembly maybe decided to not to use it with DE and HL.
Now I could be wrong because you were not specific as which assembly you are using, and in that "Exchange" were u talking about some exchange using xchg instruction, or were u exchanging using load and move operations??
@Teja Reddy • 28 Feb, 2020

The 1-byte instruction has an opcode alone. The 2 bytes instruction has an opcode followed by an eight-bit address or data. The 3 bytes instruction has an opcode followed by 16 bit address or data.

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