Motorola M68000 Betriebsanweisung PDF herunterladen (Seite 32)

18 Assembly Language Programming for the 68000 Family

Figure 2 Organization of a simple microcomputer system.

the M6800 family. The MC6800 is strictly an 8-bit processor. Motorola

attempted to bridge the gap with the MC6809, a pseudo-16-bit CPU.

The 6809 never caught on like the Intel 8086 family. However, it did gain

wide popularity in the Radio Shack Color computer.

A major issue that faces chip architects is how compatible to make

their new chips with earlier chips. It is rarely possible to make a new chip

completely compatible, at the machine code level, with prior designs. An

alternative is to make the architectures source code-compatible. With

this scheme, a programmer merely has to reassemble the program for

the new chip. He or she is then free to use the features of the new

chip in modifications to an already running program. This technique was

adopted by Motorola when they jumped to the 6809.

The successor to the Intel 8080 family is the 8086 family. Intel chose

to make the new chip family somewhat compatible at the source code

level. This requirement may have bridled the new architecture to some

extent. It is possible to convert an 8080 program to an 8086 program

by a source code conversion program. The resulting program can then

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Motorola M68000 Betriebsanweisung Seite 32