The STE-Z180 is a low-cost Z180 board for general-purpose use in STEbus systems. It can hold enough memory to run CP/M Plus. It has two memory sockets, two counter/timers, two serial ports, two DMA units, a memory-management unit and an interrupt controller. The STE-Z180 can act as the sole STEbus master in single-master systems or as a temporary master in larger systems with an external arbiter.
Two memory sockets are provided, for 512K RAMs or up to 512K ROMs. Because the Z180 has an on-chip MMU, these memory devices and STEbus memory can be relocated within the 1M byte addressing range of the Z180.
The two RS232 asynchronous serial channels can run at up to 38.4K baud and are fully programmable.
Up to five STEbus interrupts can be handled, and an STEbus Attention Request can be generated on one of four lines. A DMA request can be accepted on three lines.
Bus timeout, clock and reset function are provided. The Z180 is ideal for use both as a standalone CPU tor dedicated control applications, and as the CPU in a disk-based development system. Many software packages are available for the STE-Z180, and it can run standard Z80 machine code.
Power consumption: 5V only.
The Zilog ZS180 seems to be the last member of the 64180 family in active production.
For 33MHz clock max:
3 clocks per memory cycle = 11 MHz cycle rate.
3 clocks per instruction = 11 MHz instruction rate (one opcode).
6 clocks per instruction = 5.5 MHz instruction rate (one opcode, one data byte).
32 MHz would be more convenient , as the STEbus needs a 16 MHz system clock.
I recently bought eight Z180 chips for £5. Rated at 8 MHz so only twice as fast as a 4 MHz Z80, but will be okay for most work.
The N8VEM Z180 mark 4 seems a good starting point. That is a four-layer board with all the glue logic in TTL. Should become a lot less crowded if using GAL or FPGA.
The Z180 would be useful for applications that would benefit from 1 megabyte of memory space, such as CP/M. However, I would use my PC for development work and Z80 systems as targets to run small applications. Therefore it might be more useful to develop a faster Z80 system than a larger Z180 system.