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This manual includes hardware details and programming information for the MC68000,
the MC68HC000, the MC68HC001, the MC68008, the MC68010, and the MC68EC000.
For ease of reading, the name M68000 MPUs will be used when referring to all
processors. Refer to M68000PM/AD,
detailed information on the MC68000 instruction set.
The six microprocessors are very similar. They all contain the following features
• 16 32-Bit Data and Address Registers
• 16-Mbyte Direct Addressing Range
• Program Counter
• 6 Powerful Instruction Types
• Operations on Five Main Data Types
• Memory-Mapped Input/Output (I/O)
• 14 Addressing Modes
The following processors contain additional features:
M68000 Programmer's Reference Manual
, for
• MC68010
—Virtual Memory/Machine Support
—High-Performance Looping Instructions
• MC68HC001/MC68EC000
—Statically Selectable 8- or 16-Bit Data Bus
• MC68HC000/MC68EC000/MC68HC001
—Low-Power
All the processors are basically the same with the exception of the MC68008. The
MC68008 differs from the others in that the data bus size is eight bits, and the address
range is smaller. The MC68010 has a few additional instructions and instructions that
operate differently than the corresponding instructions of the other devices.
The MC68000 is the first implementation of the M68000 16/-32 bit microprocessor
architecture. The MC68000 has a 16-bit data bus and 24-bit address bus while the full
architecture provides for 32-bit address and data buses. It is completely code-compatible
with the MC68008 8-bit data bus implementation of the M68000 and is upward code
compatible with the MC68010 virtual extensions and the MC68020 32-bit implementation
of the architecture. Any user-mode programs using the MC68000 instruction set will run
unchanged on the MC68008, MC68010, MC68020, MC68030, and MC68040. This is
possible because the user programming model is identical for all processors and the
instruction sets are proper subsets of the complete architecture.
1.2MC68008
The MC68008 is a member of the M68000 family of advanced microprocessors. This
device allows the design of cost-effective systems using 8-bit data buses while providing
the benefits of a 32-bit microprocessor architecture. The performance of the MC68008 is
greater than any 8-bit microprocessor and superior to several 16-bit microprocessors.
The MC68008 is available as a 48-pin dual-in-line package (plastic or ceramic) and 52-pin
plastic leaded chip carrier. The additional four pins of the 52-pin package allow for
additional signals: A20, A21, BGACK, and IPL2. The 48-pin version supports a 20-bit
address that provides a 1-Mbyte address space; the 52-pin version supports a 22-bit
address that extends the address space to 4 Mbytes. The 48-pin MC68008 contains a
simple two-wire arbitration circuit; the 52-pin MC68008 contains a full three-wire MC68000
bus arbitration control. Both versions are designed to work with daisy-chained networks,
priority encoded networks, or a combination of these techniques.
A system implementation based on an 8-bit data bus reduces system cost in comparison
to 16-bit systems due to a more effective use of components and byte-wide memories and
peripherals. In addition, the nonmultiplexed address and data buses eliminate the need for
external demultiplexers, further simplifying the system.
The large nonsegmented linear address space of the MC68008 allows large modular
programs to be developed and executed efficiently. A large linear address space allows
program segment sizes to be determined by the application rather than forcing the
designer to adopt an arbitrary segment size without regard to the application's individual
requirements.
1.3MC68010
The MC68010 utilizes VLSI technology and is a fully implemented 16-bit microprocessor
with 32-bit registers, a rich basic instruction set, and versatile addressing modes. The
vector base register (VBR) allows the vector table to be dynamically relocated
The primary benefit of the MC68HC000 is reduced power consumption. The device
dissipates an order of magnitude less power than the HMOS MC68000.
The MC68HC000 is an implementation of the M68000 16/-32 bit microprocessor
architecture. The MC68HC000 has a 16-bit data bus implementation of the MC68000 and
is upward code-compatible with the MC68010 virtual extensions and the MC68020 32-bit
implementation of the architecture.
1.5MC68HC001
The MC68HC001 provides a functional extension to the MC68HC000 HCMOS 16-/32-bit
microprocessor with the addition of statically selectable 8- or 16-bit data bus operation.
The MC68HC001 is object-code compatible with the MC68HC000, and code written for
the MC68HC001 can be migrated without modification to any member of the M68000
Family.
1.6MC68EC000
The MC68EC000 is an economical high-performance embedded controller designed to
suit the needs of the cost-sensitive embedded controller market. The HCMOS
MC68EC000 has an internal 32-bit architecture that is supported by a statically selectable
8- or 16-bit data bus. This architecture provides a fast and efficient processing device that
can satisfy the requirements of sophisticated applications based on high-level languages.
The MC68EC000 is object-code compatible with the MC68000, and code written for the
MC68EC000 can be migrated without modification to any member of the M68000 Family.
The MC68EC000 brings the performance level of the M68000 Family to cost levels
previously associated with 8-bit microprocessors. The MC68EC000 benefits from the rich
M68000 instruction set and its related high code density with low memory bandwidth
requirements.
The section provide a brief introduction to the M68000 microprocessors (MPUs).
Detailed information on the programming model, data types, addressing modes, data
organization and instruction set can be found in M68000PM/AD,
Reference Manual
except that the MC68000 can directly access 16 Mbytes (24-bit address) and the
MC68008 can directly access 1 Mbyte (20-bit address on 48-pin version or 22-bit
address on 52-pin version). The MC68010, which also uses a 24-bit address, has much
in common with the other devices; however, it supports additional instructions and
registers and provides full virtual machine/memory capability. Unless noted, all
information pertains to all the M68000 MPUs.
. All the processors are identical from the programmer's viewpoint,
2.1PROGRAMMER'S MODEL
All the microprocessors executes instructions in one of two modes—user mode or
supervisor mode. The user mode provides the execution environment for the majority of
application programs. The supervisor mode, which allows some additional instructions
and privileges, is used by the operating system and other system software.
M68000 Programmer's
2.1.1 User' Programmer's Model
The user programmer's model (see Figure 2-1) is common to all M68000 MPUs. The
user programmer's model, contains 16, 32-bit, general-purpose registers (D0–D7, A0–
A7), a 32-bit program counter, and an 8-bit condition code register. The first eight
registers (D0–D7) are used as data registers for byte (8-bit), word (16-bit), and long-word
(32-bit) operations. The second set of seven registers (A0–A6) and the user stack pointer
(USP) can be used as software stack pointers and base address registers. In addition,
the address registers can be used for word and long-word operations. All of the 16
registers can be used as index registers.
The supervisor programmer's model consists of supplementary registers used in the
supervisor mode. The M68000 MPUs contain identical supervisor mode register
resources, which are shown in Figure 2-2, including the status register (high-order byte)
and the supervisor stack pointer (SSP/A7').
3116 150
158 70
CCR
A7'
SUPERVISOR STACK
(SSP)
POINTER
STATUS REGISTER
SR
Figure 2-2. Supervisor Programmer's Model Supplement
The supervisor programmer's model supplement of the MC68010 is shown in Figure 2-
3. In addition to the supervisor stack pointer and status register, it includes the vector
base register (VRB) and the alternate function code registers (AFC).The VBR is used to
determine the location of the exception vector table in memory to support multiple vector
tables. The SFC and DFC registers allow the supervisor to access user data space or
emulate CPU space cycles.
3116 150
158 70
CCR
310
20
A7'
SUPERVISOR STACK
(SSP)
POINTER
SRSTATUS REGISTER
VBRVECTOR BASE REGISTER
SFC
ALTERNATE FUNCTION
CODE REGISTERS
DFC
Figure 2-3. Supervisor Programmer's Model Supplement
(MC68010)
2.1.3 Status Register
The status register (SR),contains the interrupt mask (eight levels available) and the
following condition codes: overflow (V), zero (Z), negative (N), carry (C), and extend (X).
Additional status bits indicate that the processor is in the trace (T) mode and/or in the
supervisor (S) state (see Figure 2-4). Bits 5, 6, 7, 11, 12, and 14 are undefined and
reserved for future expansion
SYSTEM BYTEUSER BYTE
151310840
III
210
XNZVC
TRACE MODE
SUPERVISOR
STATE
INTERRUPT
MASK
S
T
Figure 2-4. Status Register
2.2DATA TYPES AND ADDRESSING MODES
The five basic data types supported are as follows:
In addition, operations on other data types, such as memory addresses, status word
data, etc., are provided in the instruction set.
The 14 flexible addressing modes, shown in Table 2-1, include six basic types:
1. Register Direct
2. Register Indirect
3. Absolute
4. Immediate
5. Program Counter Relative
6. Implied
The register indirect addressing modes provide postincrementing, predecrementing,
offsetting, and indexing capabilities. The program counter relative mode also supports
indexing and offsetting. For detail information on addressing modes refer to
M68000PM/AD,
Relative with Offset
Relative with Index and Offset
Register Indirect Addressing
Register Indirect
Postincrement Register Indirect
Predecrement Register Indirect
Register Indirect with Offset
Indexed Register Indirect with Offset
Immediate Data Addressing
Immediate
Quick Immediate
Implied Addressing
Implied RegisterEA = SR, USP, SSP, PC,
NOTES: 1. The VBR, SFC, and DFC apply to the MC68010 only
EA=Effective Address
Dn=Data Register
An=Address Register
( )=Contents of
PC = Program Counter
d8=8-Bit Offset (Displacement)
d16=16-Bit Offset (Displacement)
N=1 for byte, 2 for word, and 4 for long word. If An is the stack pointer and
1
the operand size is byte, N = 2 to keep the stack pointer on a word boundary.
¯=Replaces
Xn=Address or Data Register used as Index Register
SR=Status Register
USP =User Stack Pointer
SSP =Supervisor Stack Pointer
CP=Program Counter
VBR =Vector Base Register
EA=Dn
EA=An
EA = (Next Word)
EA = (Next Two Words)
EA = (PC)+d
EA = (PC)+d
EA = (An)
EA = (An), An ← An+N
An
¯ An–N, EA=(An)
EA = (An)+d
EA = (An)+(Xn)+d
DATA = Next Word(s)
Inherent Data
16
8
16
VBR, SFC, DFC
Dn
An
(xxx).W
(xxx).L
(d16,PC)
(d8,PC,Xn)
(An)
(An)+
-(An)
(d16,An)
8
(d8,An,Xn)
#<data>
SR,USP,SSP,PC,
VBR, SFC,DFC
2.3DATA ORGANIZATION IN REGISTERS
The eight data registers support data operands of 1, 8, 16, or 32 bits. The seven address
registers and the active stack pointer support address operands of 32 bits.
2.3.1 Data Registers
Each data register is 32 bits wide. Byte operands occupy the low-order 8 bits, word
operands the low-order 16 bits, and long-word operands, the entire 32 bits. The least
significant bit is addressed as bit zero; the most significant bit is addressed as bit 31.
When a data register is used as either a source or a destination operand, only the
appropriate low-order portion is changed; the remaining high-order portion is neither
used nor changed.
2.3.2 Address Registers
Each address register (and the stack pointer) is 32 bits wide and holds a full, 32-bit
address. Address registers do not support byte-sized operands. Therefore, when an
address register is used as a source operand, either the low-order word or the entire
long-word operand is used, depending upon the operation size. When an address
register is used as the destination operand, the entire register is affected, regardless of
the operation size. If the operation size is word, operands are sign-extended to 32 bits
before the operation is performed.
2.4DATA ORGANIZATION IN MEMORY
Bytes are individually addressable. As shown in Figure 2-5, the high-order byte of a
word has the same address as the word. The low-order byte has an odd address, one
count higher. Instructions and multibyte data are accessed only on word (even byte)
boundaries. If a long-word operand is located at address n (n even), then the second
word of that operand is located at address n+2.
1514131211109876543210
ADDRESS
$000000
$000002
$FFFFFE
BYTE 000000BYTE 000001
BYTE 000002
BYTE FFFFFE
WORD 0
WORD 1
BYTE 000003
WORD 7FFFFF
BYTE FFFFFE
Figure 2-5. Word Organization in Memory
The data types supported by the M68000 MPUs are bit data, integer data of 8, 16, and
32 bits, 32-bit addresses, and binary-coded-decimal data. Each data type is stored in
memory as shown in Figure 2-6. The numbers indicate the order of accessing the data
from the processor. For the MC68008 with its 8-bit bus, the appearance of data in
memory is identical to the all the M68000 MPUs. The organization of data in the memory
of the MC68008 is shown in Figure 2-7.
Figure 2-7. Memory Data Organization of the MC68008
2.5INSTRUCTION SET SUMMARY
Table 2-2 provides an alphabetized listing of the M68000 instruction set listed by
opcode, operation, and syntax. In the syntax descriptions, the left operand is the source
operand, and the right operand is the destination operand. The following list contains the
notations used in Table 2-2.
Immediate Data — Immediate data from the instruction
Source — Source contents
Destination — Destination contents
Vector — Location of exception vector
+inf — Positive infinity
–inf — Negative infinity
<fmt> — Operand data format: byte (B), word (W), long (L), single
(S), double (D), extended (X), or packed (P).
FPm — One of eight floating-point data registers (always
specifies the source register)
FPn — One of eight floating-point data registers (always
specifies the destination register)
Notation for subfields and qualifiers:
<bit> of <operand> — Selects a single bit of the operand
<ea>{offset:width} — Selects a bit field
(<ope ra nd >) — The contents of the referenced location
<operand>10 — The operand is binary-coded decimal, operations are
performed in decimal
(<address register>) — The register indirect operator
–(<address register>) — Indicates that the operand register points to the memory
(<address register>)+ — Location of the instruction operand—the optional mode
qualifiers are –, +, (d), and (d, ix)
#xxx or #<data> — Immediate data that follows the instruction word(s)
Notations for operations that have two operands, written <operand> <op> <operand>,
where <op> is one of the following:
→ — The source operand is moved to the destination operand
↔ — The two operands are exchanged
+ — The operands are added
– — The destination operand is subtracted from the source
operand
× — The operands are multiplied
÷ — The source operand is divided by the destination
operand
< — Relational test, true if source operand is less than
destination operand
> — Relational test, true if source operand is greater than
shifted by, rotated by — The source operand is shifted or rotated by the number of
positions specified by the second operand
Notation for single-operand operations:
~<operand> — The operand is logically complemented
<operand>sign-extended — The operand is sign-extended, all bits of the upper
portion are made equal to the high-order bit of the lower
portion
<operand>tested — The operand is compared to zero and the condition
codes are set appropriately
Notation for other operations:
TRAP — Equivalent to Format/Offset Word → (SSP); SSP–2 →
SSP; PC → (SSP); SSP–4 → SSP; SR → (SSP);
SSP–2 → SSP; (vector) → PC
STOP — Enter the stopped state, waiting for interrupts
If <condition> then — The condition is tested. If true, the operations after "then"
<operations> elseare performed. If the condition is false and the optional
<operations>"else" clause is present, the operations after "else" are
performed. If the condition is false and else is omitted, the
instruction performs no operation. Refer to the Bcc
instruction description as an example.
This section contains descriptions of the input and output signals. The input and output
signals can be functionally organized into the groups shown in Figure 3-1 (for the
MC68000, the MC68HC000 and the MC68010), Figure 3-2 ( for the MC68HC001), Figure
3-3 (for the MC68EC000), Figure 3-4 (for the MC68008, 48-pin version), and Figure 3-5
(for the MC68008, 52-pin version). The following paragraphs provide brief descriptions of
the signals and references (where applicable) to other paragraphs that contain more
information about the signals.
NOTE
The terms assertion and negation are used extensively in this
manual to avoid confusion when describing a mixture of
"active-low" and "active-high" signals. The term assert or
assertion is used to indicate that a signal is active or true,
independently of whether that level is represented by a high or
low voltage. The term negate or negation is used to indicate
that a signal is inactive or false.