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7
I ntrod uction
General
The COSMAC Microprocessor has been developed and tested within RCA in a wide variety of appli-
cations. COSMAC is suitable for use in business, education, entertainment, instrumentation, control,
communications, and other applications where stored program control is desired.
The RCA COSMAC Microprocessor is a CMOS byte-oriented central processing unit (CPU). It is suitable
for use in a wide range of stored-program computer systems or products. These systems can be either special
or general-purpose in nature. They are byte-oriented, a byte being eight bits.
COSMAC operations are specified by sequences of one-byte operation codes stored in a memory. These
operation codes are called
instructions.
Sequences of instructions, called
programs,
determine the specific
behavior or function of a COSMAC-based system. System functions are easily changed by modifying the
program(s) stored in memory.
This ability to change function without extensive hardware modification is
the basic advantage of a stored-program computer. Reduced cost results from using identical hardware
components (memory and microprocessor) in a variety of different systems or products.
The COSMAC microprocessor includes all of the circuits required for fetching, interpreting, and exe-
cuting instructions which have been stored in standard types of memories. Extensive
input/output (I/O)
control features are also provided to facilitate system design.
Microprocessor cost is only a small part of total system or product cost. Memory, input, output, power-
supply, system-control, and programming costs are also major considerations. A unique set of COSMAC
features combine to minimize the total system cost.
COSMAC's low-power, single-voltage CMOS circuitry minimizes power-supply and packaging costs.
High noise immunity and wide temperature tolerance facilitate use in hostile environments.
COSMAC compatibility with standard, high-volume memories assures minimum memory cost and
maximum system flexibility for both current and future applications. Program storage requirements are
reduced by means of an efficient one-byte instruction format.
The 40-pin COSMAC system interface is designed to minimize external I/O and memory control
circuitry. A single-phase clock, internal direct-memory-access (DMA) mode, flexible I/O instructions,
program interrupt, program load mode, and static circuitry are other COS MAC features explicitly aimed
at total system cost reduction. COSMAC does not require an external bootstrap ROM.
Microprocessor programming is facilitated by a variety of support programs or software. Extensive
support software and support hardware are available for use in developing COS MAC systems. Machine-
language programming is sometimes indicated when only a few short programs need to be developed.
COSMAC provides a set of efficient, easy-to-Iearn instructions which are simple to use.
The COSMAC microprocessor comprises two conservatively designed
LSI
chips (one 40-pin and one
28-pin dual-in-line package). Appendix C shows the required interconnections for these two
LSI
chips and
summarizes the COSMAC system interface signals.
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