C505_9708 SIEMENS [Siemens Semiconductor Group], C505_9708 Datasheet - Page 18

• Manufacturer Part Number: C505_9708
• Description: 8-Bit CMOS Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

Fundamental Structure
C505 / C505C
2.1
CPU
The C505 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 16 MHz external clock, 58% of the instructions execute in 375 ns (20 MHz
: 300 ns).
The CPU (Central Processing Unit) of the C505 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. They 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, BDC-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, it 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 C501/8051 standard microcontroller, the C505 contains
8 datapointers. For complex applications with peripherals located in the external data memory
space (e.g. CAN controller) 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.
Semiconductor Group
2-3
1997-08-01