C868_02 Datasheet, PDF (19/244 Pages) Infineon Technologies AG – 8 - Bit CMOS Microcontroller

C868
Fundamental Structure
2.1
CPU
The C868 is efficient both as a controller and as an arithmetic processor. It has extensive
facilities for binary and BCD arithmetic and excels in its bit-handling capabilities. Efficient
use of program memory results from an instruction set consisting of 44% one-byte, 41%
two-byte, and 15% three-byte instructions. With a 10.67 MHz external crystal (giving a
40MHz CPU clock), 58% of the instructions execute in 300 ns.
The CPU (Central Processing Unit) of the C868 consists of the instruction decoder, the
arithmetic section and the program control section. Each program instruction is decoded
by the instruction decoder. This unit generates the internal signals controlling the
functions of the individual units within the CPU. These internal signals have an effect on
the source and destination of data transfers and control the ALU processing.
The arithmetic section of the processor performs extensive data manipulation and is
comprised of the arithmetic/logic unit (ALU), an A register, B register and PSW register.
The ALU accepts 8-bit data words from one or two sources and generates an 8-bit result
under the control of the instruction decoder. The ALU performs the arithmetic operations
add, substract, multiply, divide, increment, decrement, BCD-decimal-add-adjust and
compare, and the logic operations AND, OR, Exclusive OR, complement and rotate
(right, left or swap nibble (left four)). Also included is a Boolean processor performing the
bit operations as set, clear, complement, jump-if-set, jump-if-not-set, jump-if-set-and-
clear and move to/from carry. Between any addressable bit (or its complement) and the
carry flag, the ALU can perform the bit operations of logical AND or logical OR with the
result returned to the carry flag.
The program control section controls the sequence in which the instructions stored in
program memory are executed. The 16-bit program counter (PC) holds the address of
the next instruction to be executed. The conditional branch logic enables internal and
external events to the processor to cause a change in the program execution sequence.
Additionally to the CPU functionality of the 8051 standard microcontroller, the C868
contains 8 datapointers. For complex applications with peripherals located in the
external data memory space or extended data storage capacity, this turned out to be a
"bottle neck" for the 8051’s communication to the external world. Especially
programming in high-level languages (PLM51, C51, PASCAL51) requires extended
RAM capacity and at the same time a fast access to this additional RAM because of the
reduced code efficiency of these languages.
Accumulator
ACC is the symbol for the accumulator register. The mnemonics for accumulator-specific
instructions, however, refer to the accumulator simply as A.
Program Status Word
The Program Status Word (PSW) contains several status bits that reflect the current
state of the CPU.
User’s Manual
2-3
V 0.4, 2002-01