M68HC11
REFERENCE MANUAL
GENERAL DESCRIPTION
MOTOROLA
1-1
SECTION 1
GENERAL DESCRIPTION
This reference manual will be a valuable aid in the development of M68HC11 applica-
tions. Detailed descriptions of all internal subsystems and functions have been devel-
oped and carefully checked against internal Motorola design documentation, making
this manual the most comprehensive reference available for the M68HC11 Family of
microcontroller units (MCUs).
Practical applications are included to demonstrate the operation of each subsystem.
These applications are treated as complete systems, including hardware/software in-
teractions and trade-offs. Interfacing techniques to prevent component damage are
discussed to aid the hardware designer. For software programmers,
SECTION 6
CENTRAL PROCESSING UNIT
and
APPENDIX A INSTRUCTION SET DETAILS
contain examples demonstrating efficient use of the instruction set.
This manual is intended to complement Motorola’s official data sheet, not replace it.
The information in the data sheet is current and is guaranteed by production testing.
Although the information in this manual was checked against parts and design docu-
mentation, the accuracy is not guaranteed like the data sheet is guaranteed. This man-
ual assumes the reader has some basic knowledge of MCUs and assembly-language
programming; it may not be appropriate as an instruction manual for a first-time MCU
user.
The information in this manual is much more detailed than would usually be required
for normal use of the MCU, but a user who is familiar with the detailed operation of the
part is more likely to find a solution to an unexpected system problem. In many cases,
a trick based on software or on-chip resources can be used rather than building ex-
pensive external circuitry. Data sheets are geared toward customary, straightforward
use of the on-chip peripherals; whereas, an experienced MCU user often uses these
on-chip systems in very unexpected ways. The level of detail in this manual will help
the normal user to better understand the on-chip systems and will allow the more ad-
vanced user to make maximum use of the subtleties of these systems.
In addition to this manual, the data sheet(s) or technical summary is needed for the
specific version(s) of the M68HC11 being used. A pocket reference guide is another
beneficial source.
1.1 General Description of the MC68HC11A8
The HCMOS MC68HC11A8 is an advanced 8-bit MCU with highly sophisticated, on-
chip peripheral capabilities. New design techniques were used to achieve a nominal
bus speed of 2 MHz. In addition, the fully static design allows operation at frequencies
down to dc, further reducing power consumption.
The HCMOS technology used on the MC68HC11A8 combines smaller size and higher