GMS34004 Datasheet, PDF (21/105 Pages) Hynix Semiconductor – 4-BIT SINGLE CHIP MICROCOMPUTERS

Chapter 2. Architecture
Y-register (Y)
Y-register has 4 bits. It operates as a data pointer or a general-purpose register.
Y-register specifies and address (a₀~a₃) in a page of data memory, as well as it
is used to specify an output port. Further it is used to specify a mode of carrier
signal outputted from the REMOUT port. It can also be treated as a general-
purpose register on a program.
Accumulator (A_CC)
The 4-bit register for holding data and calculation results.
Arithmetic and Logic Unit (ALU)
In this unit, 4bits of adder/comparator are connected in parallel as it`s main
components and they are combined with status latch and status logic (flag.)
(1) Operation circuit (ALU) :
The adder/comparator serves fundamentally for full addition and data
comparison. It executes subtraction by making a complement by processing
an inversed output of A_CC (A_CC+1)
(2) Status logic :
This is to bring an ST, or flag to control the flow of a program. It occurs when
a specified instruction is executed in two cases such as overflow in operation
and two inputs unequal.
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