8052 Instruction Set

UNDEFINED

Undefined Instruction

 

 

 

Syntax

???

 

 

 

 

 

 

 

 

 

 

 

 

 

Instructions

OpCode

Bytes

Cycles

Flags

 

 

 

 

 

 

 

 

???

0xA5

1

1

C

 

 

 

 

 

 

 

The undefined instruction is, as the name suggests, not a documented instruc- tion. The 8052 supports 255 instructions and OpCode 0xA5 is the single op- code that is not used by any documented function. It is not recommended that it be executed because it is not documented nor defined.

However, based on my research, executing this undefined instruction takes one machine cycle and appears to have no effect on the system except that the carry bit always seems to be set.

Note:

We received input from an 8052.com user that the undefined instruction real- ly has a format of Undefined bit1,bit2 and effectively copies the value of bit2 to bit1. In this case, it would be a three-byte instruction. We have not had an opportunity to verify or disprove this report, so we present it to the world as additional information.

See also: NOP

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Texas Instruments MSC1210 manual Undefined, Instructions OpCode Bytes Cycles Flags ??? 0xA5