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assemblyavr

direct Single Register Addressing AVR

I was looking at Direct Single Register Addressing in Atmel AVR instruction set. In Page# 3 of instruction Set manual, it is written that Direct Single Register Addressing instruction contains Rd in bits 0 to 4 and opcode in rest of the 12 bits. In such case where is the immediate value of 8 bits located? The figure 1 in the manual does not indicate the immediate value. Ex: LDI R18,0xff : In this instruction, if 5 bits are register address and 11 bits are Opcode, there is no immediate data!

Or is Opcode is of 4 bits and rest are all for data?

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Solution

  • The diagram you copied is only the concept of the single register addressing. You should scroll down to the concrete instructions to see how the operands are encoded.

    For example, LDI (Page 89 in this copy) uses a 4-bit opcode, 4 bits of the immediate value, then 4 bits for selecting the register, then the other 4 bits.