UPI-41A/41AH/42/42AH USER’S MANUAL
The following sections provide a detailed functional de-
scription of the UPI microcomputer. Figure 2-4 illus-
trates the functional blocks within the UPI device.
CPU SECTION
The CPU section of the UPI-41A/41AH/42/42AH
microcomputer performs basic data manipulations and
controls data flow throughout the single chip computer
via the internal 8-bit data bus. The CPU section in-
cludes the following functional blocks shown in Figure
2-4:
#
Arithmetic Logic Unit (ALU)
#
Instruction Decoder
#
Accumulator
#
Flags
Arithmetic Logic Units (ALU)
The ALU is capable of performing the following opera-
tions:
#
ADD with or without carry
#
AND, OR, and EXCLUSIVE OR
#
Increment, Decrement
#
Bit complement
#
Rotate left or right
#
Swap
#
BCD decimal adjust
In a typical operation data from the accumulator is
combined in the ALU with data from some other
source on the UPI-41A/41AH/42/42AH internal bus
(such as a register or an I/O port). The result of an
ALU operation can be transferred to the internal bus or
back to the accumulator.
If an operation such as an ADD or ROTATE requires
more than 8 bits, the CARRY flag is used as an indica-
tor. Likewise, during decimal adjust and other BCD
operations the AUXILIARY CARRY flag can be set
and acted upon. These flags are part of the Program
Status Word (PSW).
Instruction Decoder
During an instruction fetch, the operation code (op-
code) portion of each program instruction is stored and
decoded by the instruction decoder. The decoder gener-
ates outputs used along with various timing signals to
control the functions performed in the ALU. Also, the
instruction decoder controls the source and destination
of ALU data.
Accumulator
The accumulator is the single most important register
in the processor. It is the primary source of data to the
ALU and is often the destination for results as well.
Data to and from the I/O ports and memory normally
passes through the accumulator.
231318 – 9
Figure 2-4. UPI-41A/41AH/42/42AH Block Diagram
10
Содержание UPI- 41A
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