User’s Manual
2-2
05.99
Fundamental Structure
C513AO
2.1
Central Processing Unit (CPU)
The C513AO 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 crystal, 58% of the instructions execute in 750 ns.
The CPU of the C513AO consists of the instruction decoder, the arithmetic section, and the
program control section. Each program instruction is decoded by the instruction decoder. This
section generates the internal signals which control the functions of the individual units within the
CPU. They have an effect on the source and destination of data transfers, and control the
Arithmetic/Logic Unit (ALU) processing.
The arithmetic section of the processor performs extensive data manipulation and is comprised of
the ALU and registers A, B, and PSW. 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. It performs the logic operations: AND, OR, Exclusive OR, complement and
rotate (right, left or swap nibble (left four). Also included is a Boolean processor which performs the
bit operations: set, clear, complement, 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.
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 which reflect the current state of the
CPU.