SC140, v1.0, User Guide

SC140 is a Z180 based Single Board Computer in the Z50Bus card form factor. It can be used on its own as a Single Board Computer or it can be plugged into a Z50Bus backplane for expansion.

SC140 normally has Flash memory containing RomWBW in socket U1.

Documentation for RomWBW here.

A short guide to getting started with RomWBW on SC140 can be found here.

Quick Guide to Connectors

P11, shown in blue, is the Z50Bus connector. SC140 can be used as a single board computer (SBC) without being connected to a Z50Bus backplane

P1 and P2, shown in orange, is an SPI port, primarily for connecting a Micro SD card adapter. P1 is a male connector, while P2 is a female connector. You should not generally use both at the same time. They are connected exactly the same, providing a choice of male or female connection.

P5 and P6, plus P3 and P4, shown in red, are serial port A. P5 and P6 are typically used to connect an FTDI style serial adapter. P3 or P4 allow a jumper shunt to be fitted to connect power to or from the serial port.

P9 and P10, plus P7 and P8, shown in green, are serial port B. P9 and P10 are typically used to connect an FTDI style serial adapter. P7 or P8 allow a jumper shunt to be fitted to connect power to or from the serial port.

Quick Guide to Jumpers

As a quick guide to getting started: Fit jumper shunts in the positions shown below in red and supply 5 volts via the serial port shown below in green. Typically the serial port is connected to a modern computer’s USB socket using a USB to serial adapter. These adapters can supply 5 volts to SC140. A jumper shunt fitted to P3 or P4 connects power from the USB adapter to the circuitry of SC140.

And for those who are sensible enough to read User Guides…

More about power

SC140 is typically connected to a computer or terminal with an FTDI style serial adapter. This can, optionally, also provide power for SC140. However, some USB sockets and some FTDI style adapters will not provide adequate power, especially if many accessories and expansion cards are also connected.

Each serial port, highlighted below in red, can supply power to the system. To connect power from a serial port, fit a jumper shunt in the appropriate location, indicated below in yellow. The lower jumper is for port A and the upper jumper is for port B.

WARNING: You should normally only connect one power source to the system, at any time.

As power can flow either way, these jumpers also enable serial devices to be powered from SC140. If such devices are used, fit a jumper shunt in the appropriate position, indicated above in yellow.

An alternative way to power SC140 is to plug it into a powered Z50Bus backplane. In this case you are unlikely to want jumper shunts fitted to connect power to or from the serial ports.

Write Protect Flash

Jumper JP1, shown below, enables the Flash chip to be write protected. It is unlikely the Flash chip will be corrupted in normal operation due to the software requirements to write to it. However, for peace of mind you can disable writing with a jumper shunt.

Fit the shunt in the position shown below in green to disable writing (to write protect the Flash memory). Alternatively, fit the shunt in the position shown below in red to enable writing.

The Flash chip can be updated without removing it from the circuit board. This is done using the supplied FLASH utility, with write enabled using JP1. While RomWBW includes a ROM disk, the files on that disk can not be updated even with the chip write enabled. It is theoretically possible to update the files in this way, but there is no software, as far as I know, to do this.

Serial Ports

The board has two asynchronous serial ports, with software selectable baud rate. These are 5 volt FTDI style ports.

Port A (the first, default port) is highlighted below in green, and port B is highlighted in red.

Port A has hardware flow control, while port B does not. Port B lacks RTS and CTS signals as they are not available on the Z180 processor.

The pin-out, below, describes signals with respect to SC140 so an output is a signal from SC140 to a computer or terminal.

6 Clear To Send (CTS) input (not connected)
5 Transmit Data (TxD) output
4 Recieve Data (RxD) input
3 Vcc (5V) optional via jumper
2 Request To Send (RTS) output
1 Ground (GND)

The ground terminal is is at the bottom of the connector in the illustration above.

A typical FTDI style serial adapter is illustrated to the right.

This may be fitted directly to SC140 or by a 6-way adapter cable.

The default serial ports settings are as follows:

Baud rate115200 (RomWBW v3.x)
Data bits8
Stop bits1
Flow controlHardware

The default serial port connection is P5 / P6, Serial Port A.

SPI Port

The card has an SPI port, primarily for connection of an SD card adapter.

Note that the ground pin is at the ‘top’ of the SPI/SD card connector, while the serial ports have the ground pin at the ‘bottom’.

The signals are 5 volt levels, with the following pin-out.

6 Ground (GND)
5 Vcc (5V)
4 Master in, slave out
3 Master out, slave in
2 Clock
1 Chip select (active low)

The ground terminal is is at the top of the connector in the illustration above.

A typical micro SD card adapter is illustrated to the right.

This may be fitted directly to SC140 or by a 6-way adapter cable.

Expansion Bus Plug

The expansion connector is 50-pin Z50Bus compatible.

Details of the Z50Bus can be found here.

Memory Map

The physical memory map is simply 512k bytes of Flash ROM at the bottom of memory and 512k bytes of RAM at the top of memory.

The Z180’s memory management unit deals with mapping chunks of this memory into the logical 64k memory map supported by the Z80/Z180 instruction set.

0x80000 to 0xFFFFFRAM (512k bytes)
0x00000 to 0x7FFFF Flash ROM (512k bytes)

Input / Output Ports

The card’s I/O port addresses are as follows.

0xC0 to 0xFFZ180’s internal I/O registers
0x0EStatus LED port (write only)
Bit 0 = LED control (active low)
0x0DReserved for LED output port
(via expansion digital I/O module)
0x0CSystem I/O port (write only)
Bit 2 = SPI select (active low)

All other I/O addresses are available for use by expansion cards on the Z50Bus.

For details of the Z180’s internal registers, consult the Z180 datasheet. There are too many registers and functions to describe here.

The status LED is initially turned on but is otherwise free to use. The LED can be written to with output statements or instructions.

  • Turn the status LED off from BASIC:
    • OUT 14, 1
  • Turn the status LED on from BASIC:
    • OUT 14, 0

Note that the LED is turned on by writing a 0 (not a 1). This is because the LED output is active low. This is necessary to allow the LED to be turned on by a hardware reset to indicate power is present. The reset signal clears the output latch to zero, thus zero is the on state.

The optional LED output port has 8 LEDs which are used to display diagnostic information at reset, but are otherwise free for use. These can be written to with simple input and output statements or instructions.

  • From BASIC:
    • OUT 13, <byte-to-be-output>
  • From the Small Computer Monitor
    • O D <byte-to-to-output>
  • From assembler:
    • LD A, <byte-to-be-output>
    • OUT ($D), A

Homebrew 8-bit retro computing