Page 90 - DCAP210_INTRODUCTION__TO_MICROPROCESSORS

Introduction to Microprocessors

Notes The register available inside the microprocessor can be classified into; register accessible to user
and registers not accessible to the user. The registers available to the user can be further classified
into; general purpose registers and special purpose registers.

Figure 6.3: General Purpose Registers

Differentiate between internal and external architecture of microprocessor in the
term of pins.

(a) General Purpose Registers: The general-purpose registers are used for storing data as well as
the address. 8085A has six general-purpose registers. They are B, C, D, E, H and L. In 8085A
microprocessor, the data size is 8-bit and address size is 16-bit. Hence they can be used in pairs
like B-C, D-E and H-L to store 16-bit address as show in Figure 6.4.

When these registers are used in pair the higher byte will reside in first registers i.e., B, D and H
and lower byte in second registers i.e., C, E and L. For example in case of B-C pair the higher byte
will reside in B and lower byte in C register. The register pair H-L function as data pointer and
can holds memory addresses in the register indirect addressing mode.

Figure 6.4: Register Organization

(b) Special Purpose Registers: They are a set of registers provided for some specific applications.
Some of the special purpose registers are: Accumulator (A), Program Counter (PC), Stack Pointer
(SP) and Status Flags. Thus the microprocessor has six programmable registers inside the
microprocessor as shown in Figure 6.5.

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