There are only few microprocessors in the Zilog family, but they have the 8 bit, the 16 bit, and the 32 bit processors.
The Z80 microprocessor is an 8 bit CPU with a 16 bit address bus capable of
direct access of 64k of memory space. It has a language of 252 root instructions
and with the reserved 4 bytes as prefixes, acceses an additional 308 instructions.
The Z80 was modeled after the 8088 and contains the 78 - 8088 opcodes as a
subset to it's language.
Programming features include an accumulator and six eight bit registers that can be paired as 3-16 bit registers. In addition to the general registers, a stack-pointer, program-counter, and two index (memory pointers) registers are provided. While not in the same leauge as the 80486 or 68000 series, the Z80 is extremely useful for low cost control applications. One of the more useful features of the Z80 is the built-in refresh circuitry for ease of design with DRAMs.
The 68000 is the 16 bit microprocesor of Zilog. It is introduced not
long after the Intel 8086, but with superior features. Even if it was a 16
bit processor, it could address up to 23 bits in some versions by using segment
registers. The Z8000 registers could be used as sixteen 8 bit registers,
sixteen 16 bit registers, eight 32 bit registers, or four 64 bit registers.
All the registers are general purpose. It also featured two modes, one for
the operating system, and one for user programs. The user mode prevents the
user form messing with interrupt handling and other potentially dangerous
stuff. Also, like the Z80, the Z8000 featured automatic RAM refresh circuitry.
One source of problem for the Z8000 were the bugs due ot its non-usage of
microcode.
A later version, the Zilog 80000, was expanded to 32 bits internally and was fully pipelined.
