STEbus Z180 board

Z180 processor board

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Z180 or ZS180 processor
Two memory sockets
512K RAM
512K ROM
Two programmable serial ports
Two counter-timers
STEbus DMA operation
On-board and STEbus interrupts
CP/M operating system


SD card interface
PCMCIA interface


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.

  • Z180 to Z80 socket adapter

    Keith05/19/2019 at 19:33 0 comments

    I had a think, and note that most of the control signals are exactly the same as the Z80. So rather than invent a new board from scratch, I could simply wire the Z180 to the CPU socket of an existing Z80 board (like the SCPUB board),

    GND, VCC, D0-7, A0-15, !WAIT, !BUSAK, !BUSRQ, !RESET, !NMI, !HALT, !RFSH, !IORQ, !MREQ, !M1, !WR, !RD are identical, and can wire directly to the Z80 socket.

    RTS0, CTS0, DCD0, TXA0, RXA0, CKA0/DREQ0, TXA1, RXA1, CKA1/TEND0, TXS, RXS/CTS1, CKS are serial port signals that can connect to FTDI USB cables or serial port drivers.

    A16-A19 are new but uncomplicated, just extra address lines. They would have to go to large memory chips via flying wires.

    Z80 CLK of Z80 --> EXTAL
    PHI is the CPU clock output.

    Z80 INT --> INT0
    INT1, INT2 are extra interrupt lines, not needed yet.

    DREQ1, TEND1 are for DMA which I can ignore for now.

    E is for Motorola peripherals which I don't have.

    ST works with !HALT and !M1 to indicate CPU state. New states are DMA, HALT, and SLEEP.

    XTAL (crystal drive) is not used because CLK is driven.

    This doesn't look too difficult to deal with.

    Transplanting the Z180 into the existing SCPUB board could be done without having to re-write the serial port drivers. There is no reason why the existing SCC chip must be replaced by the Z180 serial ports. The BASIC interpreter ROM can continue to use the SCC.

    For a completely new board, one would want to do without the SCC for reasons of economy but I shan't be doing that just yet.

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