General Description (Continued)
Key features include an 8-bit memory mapped architecture,
a 16-bit timer/counter with two associated 16-bit registers
supporting three modes (Processor Independent PWM gen-
eration, External Event counter, and Input Capture capabili-
ties), two power saving HALT/IDLE modes with a
multi-sourced wakeup/interrupt capability, on-chip R/C oscil-
lator, high current outputs, user selectable options such as
WATCHDOG, Oscillator configuration, and power-on-reset.
1.1 EMI REDUCTION
The COP8SAx family of devices incorporates circuitry that
guards against electromagnetic interference — an increasing
problem in today’s microcontroller board designs. National’s
patented EMI reduction technology offers low EMI clock cir-
cuitry, gradual turn-on output drivers (GTOs) and internal ICC
smoothing filters, to help circumvent many of the EMI issues
influencing embedded control designs. National has
achieved 15 dB–20 dB reduction in EMI transmissions when
designs have incorporated its patented EMI reducing cir-
The COP8SAx family is based on a modified Harvard archi-
tecture, which allows data tables to be accessed directly
from program memory. This is very important with modern
microcontroller-based applications, since program memory
is usually ROM or EPROM, while data memory is usually
RAM. Consequently data tables usually need to be con-
tained in ROM or EPROM, so they are not lost when the mi-
crocontroller is powered down. In a modified Harvard archi-
tecture, instruction fetch and memory data transfers can be
overlapped with a two stage pipeline, which allows the next
instruction to be fetched from program memory while the
current instruction is being executed using data memory.
This is not possible with a Von Neumann single-address bus
The COP8SAx family supports a software stack scheme that
allows the user to incorporate many subroutine calls. This
capability is important when using High Level Languages.
With a hardware stack, the user is limited to a small fixed
number of stack levels.
1.3 INSTRUCTION SET
In today’s 8-bit microcontroller application arena cost/
performance, flexibility and time to market are several of the
key issues that system designers face in attempting to build
well-engineered products that compete in the marketplace.
Many of these issues can be addressed through the manner
in which a microcontroller’s instruction set handles process-
ing tasks. And that’s why COP8 family offers a unique and
code-efficient instruction set — one that provides the flexibil-
ity, functionality, reduced costs and faster time to market that
today’s microcontroller based products require.
Code efficiency is important because it enables designers to
pack more on-chip functionality into less program memory
space (ROM/OTP). Selecting a microcontroller with less pro-
gram memory size translates into lower system costs, and
the added security of knowing that more code can be packed
into the available program memory space.
1.3.1 Key Instruction Set Features
The COP8SAx family incorporates a unique combination of
instruction set features, which provide designers with opti-
mum code efficiency and program memory utilization.
Single Byte/Single Cycle Code Execution
The efficiency is due to the fact that the majority of instruc-
tions are of the single byte variety, resulting in minimum pro-
gram space. Because compact code does not occupy a sub-
stantial amount of program memory space, designers can
integrate additional features and functionality into the micro-
controller program memory space. Also, the majority instruc-
tions executed by the device are single cycle, resulting in
minimum program execution time. In fact, 77% of the instruc-
tions are single byte single cycle, providing greater code and
I/O efficiency, and faster code execution.
1.3.2 Many Single-Byte, Multifunction Instructions
The COP8SAx instruction set utilizes many single-byte, mul-
tifunction instructions. This enables a single instruction to ac-
complish multiple functions, such as DRSZ, DCOR, JID, and
LOAD/EXCHANGE instructions with post-incrementing and
post-decrementing, to name just a few examples. In many
cases, the instruction set can simultaneously execute as
many as three functions with the same single-byte instruc-
JID: (Jump Indirect); Single byte instruction; decodes exter-
nal events and jumps to corresponding service routines
(analogous to “DO CASE” statements in higher level lan-
LAID: (Load Accumulator-Indirect); Single byte look up table
instruction provides efficient data path from the program
memory to the CPU. This instruction can be used for table
lookup and to read the entire program memory for checksum
RETSK: (Return Skip); Single byte instruction allows return
from subroutine and skips next instruction. Decision to
branch can be made in the subroutine itself, saving code.
AUTOINC/DEC: (Auto-Increment/Auto-Decrement); These
instructions use the two memory pointers B and X to effi-
ciently process a block of data (analogous to “FOR NEXT” in
higher level languages).
1.3.3 Bit-Level Control
Bit-level control over many of the microcontroller’s I/O ports
provides a flexible means to ease layout concerns and save
board space. All members of the COP8 family provide the
ability to set, reset and test any individual bit in the data
memory address space, including memory-mapped I/O ports
and associated registers. Three memory-mapped pointers
handle register indirect addressing and software stack
pointer functions. The memory data pointers allow the option
of post-incrementing or post-decrementing with the data
movement instructions (LOAD/EXCHANGE). And 15
memory-maped registers allow designers to optimize the
precise implementation of certain specific instructions.
1.4 PACKAGING/PIN EFFICIENCY
Real estate and board configuration considerations demand
maximum space and pin efficiency, particularly given today’s
high integration and small product form factors. Microcontrol-
ler users try to avoid using large packages to get the I/O
needed. Large packages take valuable board space and in-
creases device cost, two trade-offs that microcontroller de-
signs can ill afford.
The COP8 family offers a wide range of packages and do not
waste pins: up to 90.9% (or 40 pins in the 44-pin package)
are devoted to useful I/O.