"Hardware description of the 8051 microcontrollers" - читать интересную книгу автора (Hennig-Roleff W.)

Additionally it is possible to manipulate single BITs with MOV, SETB, CLR and
CPL.


The 8051 has available conditional and unconditional jump instructions.
Subprograms may be called up. The return address will be placed by the CPU
on the stack. The stack is located in internal RAM and increases upwards
when used.


Division can only be done byte wise (8 BIT). For larger data, more complicated
procedures are necessary. The size of the internal RAM is often limiting.

As a cost effective controller, the 8051 enjoys great popularity.

2. Data and Addresses Page 2
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2. Data and Addresses:
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Arithmetic only handles numeric values : for example sizes of measurements,
calculation values, etc. As to the handling of text, the ALU will require
a numeric value to be assigned to every character.

Digital techniques work with two logic values (1=high or 0=low).
With one binary digit 2 numeric values can be selected.
With two binary digits 4 different numeric values can be represented:
0 = 00b, 1 = 01b, 2 = 10b and 3 = 11b (the "b" is a label for a binary value).

The alphabet consists of 26 characters. Distinguishing between the capital
and small letters and catering for several special values in addition,
(1 2 3..0 , + - ? ! : ; / ( ╘ ─ ┴ and so on) so we have approx. 80 values.
To be able to clearly differentiate between them at least 7 binary
digits are necessary.

The assignment of characters to numeric values has naturally been the norm.
In the ASCII standard (American Standard Code for Information
Interchange) 8 binary digits are used to represent numeric values. Such a
numeric value between 0 and 255 are designated as a BYTE. Each of its binary
digits is a BIT.

The choice of 8 bits per BYTE comes also into consideration in the
representation of numeric values for computations, for in hexadecimal
notation, this can be represented by just two digit hex numbers. Larger values
(with more digits) use several bytes.