be bypassed by jumpers on the final application board, can
provide for software and hardware debugging using actual
production units.
6.0 Architectural Overview
6.1 EMI REDUCTION
The COP8AME9 device 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 circuitry,
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-
cuitry.
6.5 ARCHITECTURE
The COP8 family is based on a modified Harvard architec-
ture, 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, EPROM or Flash, while data memory is
usually RAM. Consequently constant data tables need to be
contained in non-volatile memory, so they are not lost when
the microcontroller is powered down. In a modified Harvard
architecture, 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 architecture.
6.2 IN-SYSTEM PROGRAMMING AND VIRTUAL
EEPROM
The device includes a program in a boot ROM that provides
the capability, through the MICROWIRE/PLUS serial inter-
face, to erase, program and read the contents of the Flash
memory.
The COP8 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.
Additional routines are included in the boot ROM, which can
be called by the user program, to enable the user to custom-
ize in-system software update capability if MICROWIRE/
PLUS is not desired.
Additional functions will copy blocks of data between the
RAM and the Flash Memory. These functions provide a
virtual EEPROM capability by allowing the user to emulate a
variable amount of EEPROM by initializing nonvolatile vari-
ables from the Flash Memory and occasionally restoring
these variables to the Flash Memory.
6.6 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 the COP8 family offers a unique
and code-efficient instruction set - one that provides the
flexibility, functionality, reduced costs and faster time to mar-
ket that today’s microcontroller based products require.
The contents of the boot ROM have been defined by Na-
tional. Execution of code from the boot ROM is dependent
on the state of the FLEX bit in the Option Register on exit
from RESET. If the FLEX bit is a zero, the Flash Memory is
assumed to be empty and execution from the boot ROM
begins. For further information on the FLEX bit, refer to
Section 4.5, Option Register.
Code efficiency is important because it enables designers to
pack more on-chip functionality into less program memory
space (ROM, OTP or Flash). Selecting a microcontroller with
less program 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.
6.3 DUAL CLOCK AND CLOCK DOUBLER
The device includes a versatile clocking system and two
oscillator circuits designed to drive a crystal or ceramic
resonator. The primary oscillator operates at high speed up
to 10 MHz.. The secondary oscillator is optimized for opera-
tion at 32.768 kHz.
6.6.1 Key Instruction Set Features
The COP8 family incorporates a unique combination of in-
struction set features, which provide designers with optimum
code efficiency and program memory utilization.
The user can, through specified transition sequences
(please refer to Section 13.0 Power Saving Features), switch
execution between the high speed and low speed oscillators.
The unused oscillator can then be turned off to minimize
power dissipation. If the low speed oscillator is not used, the
pins are available as general purpose bidirectional ports.
6.6.2 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
program space. Because compact code does not occupy a
substantial amount of program memory space, designers
can integrate additional features and functionality into the
microcontroller program memory space. Also, the majority
instructions executed by the device are single cycle, result-
ing in minimum program execution time. In fact, 77% of the
instructions are single byte single cycle, providing greater
code and I/O efficiency, and faster code execution.
The operation of the CPU will use a clock at twice the
frequency of the selected oscillator (up to 20 MHz for high
speed operation and 65.536 kHz for low speed operation).
This doubled clock will be referred to in this document as
‘MCLK’. The frequency of the selected oscillator will be
referred to as CKI. Instruction execution occurs at one tenth
the selected MCLK rate.
6.4 TRUE IN-SYSTEM EMULATION
6.6.3 Many Single-Byte, Multi-Function Instructions
On-chip emulation capability has been added, which allows
the user to perform true in-system emulation using final
production boards and devices. This simplifies testing and
evaluation of software in real environmental conditions. The
user, merely by providing for a standard connector which can
The COP8 instruction set utilizes many single-byte, multi-
function instructions. This enables a single instruction to
accomplish multiple functions, such as DRSZ, DCOR, JID,
LD (Load) and
X (Exchange) instructions with post-
incrementing and post-decrementing, to name just a few
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