Texas Instruments MSC1210 User Manual

Page 310

8052 Instruction Set

E-26

UNDEFINED

Undefined Instruction

Syntax

???

Instructions

OpCode

Bytes

Cycles

Flags

???

0xA5

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.