ST20-C1 datasheet(7/205 Pages) STMICROELECTRONICS

7 / 205 page

7/205

2 Notation

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

Code: Function 8

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 8n.

2.1.3

Description

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:

Description: Bitwise AND of Areg and Breg.

2.1.4

Definition

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:

′← expression involving registers, etc.

memory_location

′← expression involving registers, etc.

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.

ST20-C1 Datasheet(PDF) 7 Page - STMicroelectronics

ST20-C1 Datasheet(HTML) 7 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL