EMAC PRIMER Instruction Manual page 11

The 8085 has many instructions which use these individual
general purpose registers. There are also instructions which
view a pair of the general purpose registers as a single 16
bit register. The register pairs that are used in these
instructions are BC, DE, and HL. When they are paired with
other registers C,E and L represent the least significant 8
bits of the register pairs (bits 0-7) and B,D and H represent
the most significant 8 bits (bits 8-15). Some instructions
view the A register and flag register (described below) as a
16 bit register called the processor status word (PSW). The
A register is the most significant 8 bits and the flag register
is the least significant 8 bits of register. The PSW is shown
with a diagram of the individual bits of the flag register,
below.
There are also registers that are dedicated to special
purposes. The registers and their descriptions are as
follows:
The stack pointer (SP) is a 16 bit register which
points to a memory location in RAM which will hold
temporary values in an area of RAM called the
stack. The stack is explained in detail in a later
lesson.
The program counter (PC) is a 16 bit register which
points to the memory location of the next machine
language instruction to be executed.
The flag register is an 8 bit register which has
individual bits, called flags, that indicate the result
of arithmetic or logical operations. Most of these
flags will be described later in the manual.
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