ST20-C1 STMICROELECTRONICS [STMicroelectronics], ST20-C1 Datasheet - Page 7

• Manufacturer Part Number: ST20-C1
• Description: Instruction Set Reference Manual
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

For primary instructions the code stored in memory is determined partly by the value
of the operand to the instruction. In this case the op-code is shown as ‘Function x ’
where x is the function code in the last byte of the instruction. For example, adc ( add
constant ) is shown as
This means that adc 1 would appear in memory as the hexadecimal byte value 81. For
an operand n in the range 0 to 15, adc n would appear in memory as 8 n .
2.1.3
The description section provides an indication of the purpose of the instruction as well
as a summary of the behavior. This may include details of the use of registers, whose
initial values may be used as parameters and into which results may be stored.
For example, the and instruction contains the following description:
2.1.4
The definition section provides a formal description of the behavior of the instruction.
The behavior is defined in ter ms of its effect on the state of the processor, i.e. the
changes in the values in registers and memory before and after the instruction has
executed.
The effects of the instruction on registers, etc. are given as statements of the following
form:
Primed names (e.g. Areg ) represent values after instruction execution, while names
without primes represent values when the instruction execution starts. For example,
Areg represents the value in Areg before the execution of the instruction while Areg
represents the value in Areg afterwards. So the example above states that after the
instruction has been executed the register or memory location on the left hand side
holds the value of the expression on the right hand side.
Only the changed registers and memory locations are given on the left hand side of
the statements. If the new value of a register or memory location is not given then the
value is unchanged by the instruction.
The description is written with the main function of the instruction stated first. For
example the main function of the add instruction is to put the sum of Areg and Breg
into Areg). This is followed by the other effects of the instruction, such as rotating the
stack. There is no temporal ordering implied by the order in which the statements are
written.
Code: Function 8
Description
Description: Bitwise AND of Areg and Breg.
Definition
register
memory_location
expression involving registers, etc.
expression involving registers, etc.
2 Notation
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