SC700 Series

This page outlines the options available in the SC700 series of modules and backplanes for the 80-pin RCBus. This range uses the full 80-pin RCBus for maximum functionality and future proofing.

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

The designs are open source with full details of the schematics, printed circuit board Gerber files, and software, either on this website or linked from this site. Kits are available for those who would like the convenience and reassurance that kits offer.

SC700 series photo gallery

A good place to start is one of the base systems:

These are functional computers that can be purchased, as kits, in their default configurations and used without further study of the growing range of compatible products. These systems are presented with a number of simple options, such as the backplane size. If in doubt just go with the default configurations.

If you are feeling confident then you can configure your system from scratch with the modules and backplanes listed below. You can even mix and match modules and backplanes designed for the 40-pin RCBus, the 60-pin RCBus, the 80-pin RCBus, and RC2014 products and third party “designed for RC2014” products. You will need to examine these products carefully to make sensible choices.

The following designs are available in the SC700 series.

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

SC700 series PCBs are offered in a range of colours (B=Blue, G=Green, K=Black, W=White, R=Red) as individual boards and, in some cases, as parts of kits. In addition, the design files are available for you to have your own boards manufactured in these or other colours.

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

B=Blue, G=Green, K=Black, W=White, R=Red

† SC126 is not part for the SC700 series but it is so close to what I would now design for the SC700 series it is not worth changing.

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 with plugin modules.

Motherboards

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

Motherboards	*SC720*	SC126 †
CPU	Z80	Z180
Clock (MHz)	7.3728	18.432
Reset	Yes	Yes
Supervisor	Yes	Yes
Power in via serial	Yes 5 volts	Yes 5 volts
Power in connector	Yes 8 to 15 volts	Yes 5 volts
Power in via module	No	optional
RAM (kB)	512	512
ROM (kB)	2 x 512k	2 x 512k
Firmware	1/ RomWBW 2/ SCM	1/ RomWBW 2/ SCM
Serial ports	2	2
Baud rate	115200	115200
Status LEDs	11	9
Storage	CF card	SD card
Storage via module	–	CF card (option)
Other	None	None
Vertical bus sockets	2	2
Horizontal bus socket	Yes	Yes

† SC126 is not part for the SC700 series but it is so close to what I would now design for the SC700 series it is not worth changing.

RomWBW includes CP/M and a range of other useful software. It has been produced by Wayne Warthen and included with his permission, free of charge.

SCM is the Small Computer Monitor – a capable monitor for software and hardware development and debugging.

Systems

To make it easier to select the required parts the following are available as complete systems. The details below are for the systems with default options selected when purchasing. In some cases there are options for alternative modules and backplanes to customise the system.

*Systems*	*SC791*	*SC792*	SC794
Configuration described here	default	default	default
CPU	Z80	Z180	Z80
Clock (MHz)	7.3728	18.432	7,3728
Reset	Yes	Yes	Yes
Supervisor	Yes	Yes	Yes
Power in via serial	Yes 5 volts	Yes 5 volts	Yes 5 volts
Backplane power in connector	No	Yes 5 volts	Yes 5 volts
Power in via module	Yes 8 to 15 volts	optional	optional
RAM (kB)	512	512	512
ROM (kB)	512	512 x 2	512 x 2
Firmware	RomWBW	RomWBW SCM	RomWBW SCM
Serial ports	2	2	2
Baud rate	115200	115200	115200
Status LEDs	3	2	4
Storage	CF card	SD card	CF card
Storage via module	–	CF card (optional)	–
Other	None	None	None
Free bus sockets	3	5	3
Horizontal bus socket	Yes	Yes	Yes
Backplane	SC701	SC701	SC701
Modules	SC706 SC714 SC715 SC716	SC721 SC722	SC716 SC721 SC729 SC730

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 or a module.

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

Other backplanes	*SC723*
Bus pins	80
Vertical sockets	3
Horiontal socket	No
Horzontal plug	No
Power input	5 volt 1 amp
Reset	Yes
Supervisor	Yes
Module spacing	0.6″ 15.24mm

Power supply

There are several ways to power an SC700 series system:

From a Serial to USB 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.

SC701- Modular backplane with 5-volt power input and a reset circuit

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.

SC703 – Power supply module, with reset circuit and status 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:

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	SC730
CPU	Z80	Z80	Z80
Clock (MHz)	7.3728	7.3728	7.3728
Reset button	Yes	Yes	No
Supervisor	Option	No	No
RAM (kB)	None	128k	None
ROM (kB)	None	128k	None
Serial ports	None	9600 baud bit-bang	None
Baud rate	n/a	9600	n/a
Firmware	None	SCM BASIC CP/M loader	None
Status LEDs	None	1	None
Other	Clock (option)	None	Memory management unit (MMU)

Processor modules	*SC722*
CPU	Z180
Clock (MHz)	18.432
Reset button	No
Supervisor	No
RAM (kB)	None
ROM (kB)	None
Serial ports	2
Baud rate	115200 selectable
Firmware	None
Status LEDs	1
Other	SPI for SD card MMU

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	*SC721*
RAM (kB)	128	512	512
ROM (kB)	128	512	512
Fimrware	SCM	RomWBW	RomWBW SCM
For CPU	Z80	Z80	Z180 (SC722) Z80 (SC730)
Status LEDs	2	None	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*	*SC725*
Ports	1	2	2
Baud rate	115200	115200	115200
Baud rate control	No	No	Yes
Device	68B50 ACIA	Z80 SIO/2	Z80 SIO/2 Z80 CTC
Extras	None	None	Timers

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*	SC729	SC734 †
Device	Compact- Flash	Compact- Flash	Micro SD Card
OS support	CP/M RomWBW	CP/M RomWBW	RomWBW inc. CP/M

† Support requires RomWBW v3.5 or a customised earlier version.

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 inputs 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*	SC724	SC733
Features	03″ & 0.6″ DIL layout	03″ & 0.6″ DIL layout – Flexible address decoder	03″ & 0.6″ DIL layout

Other modules

Other modules	*SC704*	*SC718*
Features	I2C bus master	Z80 CTC Counters Timers Interrupts Frequency

Other modules	SC731	*SC732*
Features	Two channel pulse width modulation (PWM) outputs	Two channel servo controller

*RCBus 80-pin products*
Backplanes	Kit	R	B	G	K	W
SC701 – 6+1 slot, 5V in
SC702 – 6+1 slot
SC709 – 12+1 slot, 5V in
SC710 – 12+1 slot
SC723 – 3 slot, 5V in
Motherboards	Kit	R	B	G	K	W
SC720 – Motherboard
Power supply modules	Kit	R	B	G	K	W
SC703 – Power, 12V in
SC712 – Power, 5V in
Processor modules	Kit	R	B	G	K	W
SC706 – Z80 CPU
SC708 – Z80 SBC
SC722 – Z180 CPU
SC730 – Z80 CPU+MMU
Memory modules	Kit	R	B	G	K	W
SC707 – Z80 mem, 128k
SC714 – Z80 mem, 512k
SC721 – Memory, 512k
Storage modules	Kit	R	B	G	K	W
SC715 – Compact Flash
SC729 – Compact Flash
SC734 – Micro SD Card
Serial port modules	Kit	R	B	G	K	W
SC705 – 68B50 ACIA
SC716 – Z80 SIO/2
SC725 – Z80 SIO/2+CTC
Digital I/O modules	Kit	R	B	G	K	W
SC719 – 8 in, 8 out
SC717 – Z80 PIO
Prototyping modules	Kit	R	B	G	K	W
SC711 – Prototyping
SC724 – Breakout
SC733 – Prototyping
Other modules	Kit	R	B	G	K	W
SC704 – I2C master
SC718 – Z80 CTC
SC726 – Clock
SC727 – RTC
SC728 – Module Riser
SC731 – Dual PWM
SC732 – Dual servo
Base systems	Kit	R	B	G	K	W
Z80 SBC/motherboard SCM & RomWBW CP/M SC720
Z180 SBC/motherboard SCM & RomWBW CP/M SC126 †
Z80 modular system RomWBW CP/M SC791
Z180 modular system SCM & RomWBW CP/M SC792
Z80 modular system SCM & RomWBW CP/M SC794

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