- Fact:
- An assembler program needs to use the resources of the CPU to perform the program operations
Therefore:
- An assembler programmer
(= a person that
write
assembler programs
needs to
know:
- The internal details of the CPU !!!
- Programming
in assembler language
is like "speaking to a machine"
and "tell the machine what to do".
You need to know the internal details of the machine before you can tell it what to do...
- 16 bits means:
the data bus has
16 wires
(Each data transfer between CPU and memory will transfer 2 bytes of data)
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- M68000
CPU has the following
logical structure:
- The M68000 CPU has the
following
General Purpose
Registers:
- 8 Data Registers
- The data registers are:
D0, D1, D2, D3, D4, D5, D6, D7
- Each data register contains
32 bits
- Primary usage
of a data register:
- store operands for operations
- The data registers are:
D0, D1, D2, D3, D4, D5, D6, D7
- 8 Address Registers
- The address registers are:
A0, A1, A2, A3, A4, A5, A6, A7
- Each address register contains
32 bits
- Primary usage
of address registers:
- store the base address of a memory location that is used as the starting point to access structured variables (such as arrays and linked lists) in memory.
Notes on address registers:
- A (every) address
must be represented using
32 bits:
- The leading zero of a
binary number must
be explicitly
expressed !!
Example:
- The value 3 in 32 bits must be expressed as: 00000000 00000000 00000000 00000011
- The leading zero of a
binary number must
be explicitly
expressed !!
- The address register A7
is special
- Address register A7 is the program stack pointer (more later)
- Do not use A7 in your program until you have learned about the system stack !!!
- The address registers are:
A0, A1, A2, A3, A4, A5, A6, A7
Note:
- The other registers MAR, MBR, PC, IR and PSR were explained previously: click here
- 8 Data Registers