This page outlines the options available in the RCBus compatible, SC700 series of modules and backplanes.

The SC700 series includes products designed to meet the requirements of the RCBus v1.0 specification.

The RCBus is an extended version of the RC2014 bus. The RCBus has been created for three main reasons:

1. To overcome the limitations of the RC2014 bus whilst maintaining compatibility with existing products. This includes support for advanced features, such as the Z80 interrupt priority chain, and support for other processor families.
2. To avoid confusion over what is an RC2014 product and what is a third party RC2014 compatible product.
3. To reduce the chance of trademark infringement. RC2014 is a trademark belonging to RFC2795 Ltd.

Modules designed for RC2014 can be used with RCBus backplanes, but not all RCBus modules can be used with RC2014 backplanes.

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Obviously, the most important question is: “What colour should it be?”

SC700 series PCBs are offered in a range of colours as individual boards and as parts of kits. In addition, the design files are available for you to have your own boards manufactured in other colours.

Below is a list of SC700 series products designed for the RCBus.

RCBus products
Backplanes	Red	Blue	Green	Black	White
SC701 – 6+1 slot, 5V in
SC702 – 6+1 slot
SC709 – 12+1 slot, 5V in
SC710 – 12+1 slot
Motherboards	Red	Blue	Green	Black	White
SC720 – Motherboard
Power supply modules	Red	Blue	Green	Black	White
SC703 – Power, 12V in
SC712 – Power, 5V in
Processor modules	Red	Blue	Green	Black	White
SC706 – Z80 CPU
SC708 – Z80 SBC
Memory modules	Red	Blue	Green	Black	White
SC707 – Z80 mem, 128k
SC714 – Z80 mem, 512k
Storage modules	Red	Blue	Green	Black	White
SC715 – Compact Flash
Serial port modules	Red	Blue	Green	Black	White
SC705 – 68B50 ACIA
SC716 – Z80 SIO/2
SIO + CTC ? TODO?
Digital I/O modules	Red	Blue	Green	Black	White
SC719 – 8 in, 8 out
SC717 – Z80 PIO
Prototyping modules	Red	Blue	Green	Black	White
SC711 – Prototyping
Other modules	Red	Blue	Green	Black	White
SC704 – I2C master
SC718 – Z80 CTC

Most RC2014 compatible modules can be used in an RCBus system.

You can make your system with a mix of colours if you really want to stand out from the crowd or if you can’t make your mind up!

With the difficult colour decision out of the way, the next question is; “What do you want to do with your retro computer?”

Consider the following questions:

• Do you want to just run existing software?
• Do you want to write software?
• Do you want to experiment with hardware?
• Do you want your system in a neat box?
• Will you be making changes to the hardware over time?
• How authentic (retro) do you want your system?
• Do you want to run CP/M?
• Do you want to run RomWBW?

What bits do you need?

A typical minimal system requires:

• Backplane (to connect the modules)
• Power supply
• Reset circuit
• A clock
• A central processing unit (CPU)
• Memory (RAM and ROM)
• A serial port

These functions can all be provided on a single motherboard or they can be split in a variety of ways on a number of modules. Additional functions can be added by plugin modules.

Motherboards

Motherboards are essentially a single board computer (SBC) with bus sockets for expansion. All SC700 series motherboards have a horizontal bus connectors to allow modular backplane sections to be added.

Motherboards	SC781
CPU	Z80
Clock (MHz)	7.3728
Reset	Yes
Supervisor	Yes
Power in via serial	Yes 8-15 volts
Power in connector	Yes
Power in via module	No
RAM (kB)	512
ROM (kB)	2 x 512k
Firmware	RomWBW
Serial ports	2
Baud rate	115200
Status LEDs	11
Storage	CF card
Storage via module	–
Other	None
Vertical bus sockets	2
Horizontal bus socket	Yes

Backplanes

Most SC700 series backplanes can be extended by joining backplane sections together. These backplanes have a number of vertical connectors for modules plus a horizontal connector for an additional backplane section.

The horizontal connector can also accept a module, which makes it more accessible for experimenting and debugging hardware.

Modular backplanes	SC701	SC702	SC709	SC710
Bus pins	80	80	80	80
Vertical sockets	6	6	12	12
Horiontal socket	Yes	Yes	Yes	Yes
Horzontal plug	No	Yes	No	Yes
Power input	5 volt 1 amp	No	5 volt 1 amp	No
Reset	Yes	No	Yes	No
Supervisor	Yes	No	Yes	No
Module spacing	0.6″ 15.24mm	0.6″ 15.24mm	0.6″ 15.24mm	0.6″ 15.24mm

Power supply

There are several ways to power an SC700 series system:

• From a USB to serial adapter. SC700 series serial ports have a 5-volt input pin which can be used to power the system. This works for modest size systems but isn’t ideal.

• From a backplane. Backplanes can include a power input connector. This is generally preferable to powering from a serial port.

• Another option is to power an SC700 series system from a power module. Power modules also provide a good quality clean reset signal and status indicator lights.

The first method of powering the system typically takes the power from a modern computer via a USB socket. The other two methods generally require a wall-mounted (wall-wart) power adapter.

Power modules	SC703	SC712
Voltage input	8-12 volt	5 volt
Max current	1 amp	1 amp
Reset	Yes	Yes
Supervisor	Yes	Yes
Status LEDs	2	2

Processor

The SC700 series offers a choice of two microprocessors: (or at least it will do soon!)

• The Z80 was extremely popular in the late 70s and 80s.

• The Z180 was introduced later as advances in integrated circuit manufacture allowed more complex designs.

The Z180 is essentially software compatible with the Z80 but includes extra functions such as serial ports. The Z180 allows physically smaller systems to be created and also reduces the system cost.

If you want a system nearest to an authentic 1980 computer you should use the Z80 processor. If you are willing to use later technology then a Z180 based system will be a good choice.

Processor modules	SC706	SC708
CPU	Z80	Z80
Clock (MHz)	7.3728	7.3728
Reset	Yes	Yes
Supervisor	Yes	Optional
RAM (kB)	None	128k
ROM (kB)	None	128k
Serial ports	None	9600 baud bit-bang
Baud rate	n/a	n/a
Firmware	None	SCM BASIC CP/M loader

Memory

Typical Z80 systems in 1980 had 64k bytes of RAM. It is possible to have more than 64k bytes of RAM on a Z80 system but it is easier to implement significantly larger memory maps with the Z180 processor.

Memory modules	SC707	SC714
RAM (kB)	128	512
ROM (kB)	2 x 32	512
Fimrware	SCM	RomWBW
For CPU	Z80	Z80
Status LEDs	2	None

Serial ports

Most systems include at least one serial port. This allows the retro computer to use a terminal, or modern computer acting as a terminal, as the main user interface.

Serial modules	SC705	SC716
Ports	1	2
Baud rate	115200	115200
Baud rate control	None	None
Device	68B50 ACIA	Z80 SIO/2
Extras	None	None

Storage

If you want to load and save files you will need some form of storage. While it is possible to transfer data to and from a modern computer via a serial port, it is generally better to have some local storage on the retro computer.

Storage modules	SC715
Device	Compact Flash
OS support	CP/M RomWBW

Digital I/O modules

Digital input/output modules can include signals to interface to external electronics and/or LEDs and switches. Input/output signals can either be fixed input or outputs, or they can be programmable bi-directional signals.

Digital I/O modules
Digital I/O modules	SC717	SC719
Device	Z80 PIO	74 series logic
Bi-directional signals	Yes (16)	None
Signal outputs	None	Yes (8)
Output LEDs	None	Yes (8)
Signal inputs	None	Yes (8)
Input LEDs	None	Yes (8)

Prototyping modules

Prototyping modules	SC711
Features	03″ & 0.6″ DIL layout

Other modules

Other modules	SC704
Features	I2C bus