Z8

Zilog Z8 - eZ8 (current design)

Micro-controller has cpu, memories, and I/O interface all on same chip.

Supports pipelining.

Three address spaces
  Register file - a memory module containing a large number of registers.
    Different from memory as multiple registers can be accessed at same time.
    Also, input and output for different registers can occur at same time.  
    Not all registers available at same time.

    Arranged as 
      4 I/O ports
      124 general purpose registers (236 in some models).
        (Grouped in 16 Register units, segmented but not overlapping,
            see register pointer)

      9 peripheral registers
      7 control registers.
           (Register pointer, CCR, stack pointer, etc).

      Can be accessed as 8 bit register or 16 bit even/odd pair Big-endian.
      4K of register space can be directly addressed using 12 bit @.

      eZ8 - 4K of register space.  Peripheral and control registers stored
        at the upper end of the register space.

Harvard Architecture (Modified?)
  Separate program. 
    Program memory on chip.
      Either permanent ROM.
      Or RAM which can also store program data.

    Up to 64K of memory with 1st 2 to 4 K on Z8 chip itself.
      Addessable by the program counter.

    1st 16 bytes of memory reserved for interrupt pointers. 
      This can be tied to external ROM to preset interrupts.  
 
  Data memory 
    Up to 64K of externally addressable memory accessed using port 0 and 1. 
    Program counter cannot address this so cannot contain code.