HPC46400E CPU
The HPC46400E CPU has a 16-bit ALU and six 16-bit regis-
ters.
Arithmetic Logic Unit (ALU)
The ALU is 16 bits wide and can do 16-bit add, subtract and
shift or logic AND, OR and exclusive OR in one timing cycle.
The ALU can also output the carry bit to a 1-bit C register.
Accumulator (A) Register
The 16-bit A register is the source and destination register
for most I/O, arithmetic, logic and data memory access op-
erations.
Address (B and X) Registers
The 16-bit B and X registers can be used for indirect ad-
dressing. They can automatically count up or down to se-
quence through data memory.
Boundary (K) Register
The 16-bit K register is used to set limits in repetitive loops
of code as register B sequences through data memory.
Stack Pointer (SP) Register
The 16-bit SP register is the stack pointer that addresses
the stack. The SP register is incremented by two for each
push or call and decremented by two for each pop or return.
The stack can be placed anywhere in user memory and be
as deep as the available memory permits.
Program (PC) Register
The 16-bit PC register addresses program memory.
Addressing Modes
ADDRESSING MODESDACCUMULATOR AS
DESTINATION
Register Indirect
This
HPC46400E (instructions are single-byte). The operand is
the memory addressed by the B register (or X register for
some instructions).
is
the
‘‘normal’’
mode
of
addressing
for
the
Direct
The instruction contains an 8-bit or 16-bit address field that
directly points to the memory for the operand.
Indirect
The instruction contains an 8-bit address field. The contents
of the WORD addressed points to the memory for the oper-
and.
Indexed
The instruction contains an 8-bit address field and an 8- or
16-bit displacement field. The contents of the WORD ad-
dressed is added to the displacement to get the address of
the operand.
Immediate
The instruction contains an 8-bit or 16-bit immediate field
that is used as the operand.
Register Indirect (Auto Increment and Decrement)
The operand is the memory addressed by the X register.
This mode automatically increments or decrements the X
register (by 1 for bytes and by 2 for words).
Register Indirect (Auto Increment and Decrement) with
Conditional Skip
The operand is the memory addressed by the B register.
This mode automatically increments or decrements the B
register (by 1 for bytes and by 2 for words). The B register is
then compared with the K register. A skip condition is gener-
ated if B goes past K.
ADDRESSING MODESDDIRECT MEMORY AS
DESTINATION
Direct Memory to Direct Memory
The instruction contains two 8- or 16-bit address fields. One
field directly points to the source operand and the other field
directly points to the destination operand.
Immediate to Direct Memory
The instruction contains an 8- or 16-bit address field and an
8- or 16-bit immediate field. The immediate field is the oper-
and and the direct field is the destination.
Double Register Indirect using the B and X Registers
Used only with Reset, Set and IF bit instructions; a specific
bit within the 64 kbyte address range is addressed using the
B and X registers. The address of a byte of memory is
formed by adding the contents of the B register to the most
significant 13 bits of the X register. The specific bit to be
modified or tested within the byte of memory is selected
using the least significant 3 bits of register X.
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