MA2901

1

The MA2901 is an industry standard 4-bit microprocessor

slice It provides a set of ALU functions selected by microcode

data applied to the inputs. The device is cascadable to handle

any word length. It can be used as a building block in the

construction of microcomputers and controllers tailored to

meet specialised applications.

Dual Address Architecture

Machine cycles are saved by simultaneous, independent

access to two working registers.

ALU has Eight Functions

Operations performed are addition, two subtractions and five

logic functions on two source operands.

Four State Flags

Zero, negative, carry and overflow.

Left / Right Shift is Independent of ALU

Only one cycle taken for add and shift operations.

Expandable

Any number of MA2901 units can be connected together to

achieve longer word lengths.

Micro Programmable

Three groups, each of three bits, for ALU function, source

operand and destination control.

DS3576-3.3

MA2901

RADIATION HARD 4-BIT MICROPROCESSOR SLICE

OPERATION

A detailed block diagram of the microprogrammable

microprocessor structure is shown in figure 1. The circuit is a

four-bit slice, cascadable to any number of bits. Therefore, all

data paths within the circuit are four bits wide. The two key

elements in the figure 1 are the 16-word by 4-bit 2-port RAM

and the high speed ALU.

Data from any of the 16 words of the Random Access

Memory (RAM) can be read from the A-port of the RAM as

controlled by the 4-bit A-address field input. Likewise, data

from any of the 16 words of the RAM as defined by the B-

address field input can be simultaneously read from the B-port

of the RAM. The same code can be applied to the A-select field

and B-select field in which case the identical file data will

appear at both the RAM A-port and B-port outputs

simultaneously.

When enabled by the RAM write enable (RAM EN), new

data is always written into the file (word) defined by the B-

address field of the RAM. The RAM data input field is driven by

a 3-input multiplexer. This configuration is used to shift the

ALU output data (F) if desired. This three-input multiplexer

scheme allows the data to be shifted up one bit position,

shifted down one bit position, or not shifted in either direction.

The RAM A-port data outputs and RAM B-port data outputs

drive separate 4-bit latches. These latches hold the RAM data

while the clock input is LOW. This eliminates any possible race

conditions that could occur while new data is being written into

the RAM.

The high-speed Arithmetic Logic Unit (ALU) can perform

three binary arithmetic and five logic operations on the two 4-

bit input words R and S. The R input field is driven from a 2-

input multiplexer, while S input field is driven from a 3-input

multiplexer. Both multiplexers also have an inhibit capability;

that is, no data is passed. This is equivalent to a “zero” source

operand.

The ALU R-input multiplexer has the RAM A-port and the

direct data inputs (D) connected as inputs. Likewise, the ALU

S-input multiplexer has the RAM A-port, the RAM B-port and

the Q register connected as inputs.

FEATURES

s Fully Compatible with Industry Standard 2901

s CMOS SOS Technology

s High SEU Immunity and Latch-up Free

s High Speed

s Low Power

FEBRUARY 1995