SC516, v1.0, User Guide

SC516 is a Z80 processor card designed for Z50Bus.

The card can be used in two basic ways:

  • As a Single Board Computer (SBC).
  • As the processor card in a Z50Bus system.

Single Board Computer

This card can be used in a modest say as a Single Board Computer. The card is connected to a computer or terminal with an FTDI style serial adapter. The adapter also provides the 5V 100mA power for the card. A reset signal will also need to be provided.

This serial port is very basic, providing only a software-generated 9600 baud, 8 data bit, 1 stop bit, no parity serial interface. It is designed to provide a very low-cost ‘starter’ port to get the system up and running as easily and cheaply as possible. It is suitable for simple applications, but a more capable serial module should be added for sophisticated applications such as running CP/M.

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

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

Z50Bus System

A more capable system can be created using this card as the processor and memory for a Z50Bus computer.

The most likely first addition would be an SC511, Serial card. This provides two asynchronous serial ports, software controlled baud rates, and a timer.

Status LED

When using the Small Computer Monitor ROM, pressing the reset button should cause the status LED to flash off and on again, either once or twice.

  • One flash off and on indicates a serial module has been detected on the bus and is being used to connect to a terminal. Serial cards usually work at 115200 baud, 8 data bits, 1 stop bit, no parity and hardware flow control (RTS/CTS).
  • Two flashes off and on indicate a serial card has not been detected and the onboard serial port (P1) is being used to connect to a terminal. This port works at 9600 baud, 8 data bits, 1 stop bit, no parity and hardware flow control (RTS/CTS).
  • If the LED continues to flash the self-test has failed, most likely indicating the RAM is not working.

Quick Start Guide

Below is a very brief guide to getting started with the SC516, Z80 Processor Card. For further details so the SC516 User Guide.

The ROM should contain the Small Computer Monitor.

It is assumed that this card is plugged into a Z50Bus compatible backplane, and that power and reset are provided to the backplane. This can either be from a dedicated power supply card (such as SC502) or from a backplane with its own power supply (such as SC513).

With power provided from the backplane, there should not be a jumper shunt connected to JP1. This jumper allows the system to be powered from the serial port, but you should only have one power source connected at a time.

Connect a suitable FTDI style TTL level serial to USB adapter from P2 to a USB socket on a PC (or similar). These adapters come in many different shapes and sizes. The picture below shows one possible configuration.

Press the system’s reset button and check the LED lights. It should flash off and on again, twice, and then remain on.

Start a suitable terminal emulation program, such as Tera Term, on the PC (or equivalent). Configure the PC’s serial port for 9600 baud, 8 data bits, 1 stop bit, no parity, and hardware flow control (RTS/CTS). There is no need to set the terminal software to add delays. Almost any terminal emulation should work with the Small Computer Monitor.

Press the system’s reset button. You should see the terminal program display something like “Small Computer Monitor”.

You are now ready to play!

Homebrew 8-bit retro computing