SC709 – RCBus Backplane

SC709 is an RCBus modular backplane with 12 vertical bus sockets, 1 horizontal bus socket, and a 5-volt power input.



Nothing known


KitsWebsiteShips from
Stephen C CousinsTindieUK
PCBsWebsiteShips from
Stephen C CousinsTindieUK
Assembled and TestedWebsiteShips from
Not available
See parts list

Parts List

PCB1SC709, v1.0, PCB
C1 to C1212Capacitor, ceramic, 100 nF
C131Capacitor, electrolytic, 100 µF
C141Capacitor, ceramic, 1 nF
JP12 to JP22
17Header, male, 2 row x 3 pin, straight
JP2,4,6,8,105Header, male, 2 row x 5 pin, straight
JP23 plus P11Header, male, 1 row x 4 pin, angled
Jumper77Jumper shunt
J11Socket, power, barrel, 2.1mm
J21Screw terminal, 2 way, 5.08mm pitch
K1 to K1212Header, female, 2 row x 40 pin, straight
LED11LED, green, 3mm
P1see JP23
R11Resistor, 1k, 0.25W
R21Resistor, 10k, 0.25W
S11Header, female, 2 row x 40 pin, angled
SW11Switch, toggle, sub-miniature, SPDT
SW21Switch, tactile button, straight
U11DS1233-5+ supervisor
Spacer12Spacer, 10mm, M3, nylon
Screw (for spacer)24Machine screw, 6mm, M3

Printed Circuit Board


This backplane conforms fully to the RCBus specification v1.0 and thus supports: RCBus-2014, RCBus-Z80, RCBus-68xx, RCBus-9995.

User Guide

The backplane can supply power to the whole RCBus system by connecting a regulated 5 volt supply to either J1 or J2. J1 is a 2.1mm barrel socket, centre positive, while J2 is a pair of screw terminals.

The regulated 5 volt supply must provide a voltage between 4.75 and 5.25 volts, and must be able to maintain that voltage at the maximum current drawn by the RCBus system, typically 500 mA, but possibly higher.

Power is connected to the modules when the ON/OFF switch, SW1, is in the ON position. The LED lights

Header pins P1 allow an external reset switch to be connected to the backpane.

The voltage supervisor and reset device (U1) provides a reliable power up reset. It works by holding the CPU in reset until the supply voltage reaches approximately 4.75 volts. If the system does not seem to be working, always check the supply voltage is above 4.75 volts on the PCB and that the RESET signal is a logic high voltage, typically above 4 volts. The supervisor should hold the reset low of about 0.5 seconds after the system is turned on and after the reset button is released.

The system should only include one enabled voltage supervisor, so the backplane includes header pins, JP23, to enable the supervor to be connected (jumper shunt fitted) or disabled (jumper shunt not fitted). Normally, it should be connected, but if you have a supervisor on another module you may need to isolate this one.

Input/output port functions
I/O Address ReadWrite
Jumper options
JP 1, 3, 5,
7, 9, 11
JPx.1 Connect P37 signal between bus sockets
JPx.2 Connect P38 signal between bus sockets*
JPx.3 Connect P39 signal between bus sockets*
* See daisy chain details below
JP 2, 4, 6,
8, 10
JPx.1 Connect TX signal between bus sockets
JPx.2 Connect RX signal between bus sockets
JPx.3 Connect P37 signal between bus sockets
JPx.4 Connect P38 signal between bus sockets*
JPx.5 Connect P39 signal between bus sockets*
* See daisy chain details below
JP12 to 22JPx.1 Connect P42 signal between bus sockets*
JPx.2 Connect P43 signal between bus sockets*
JPx.3 Connect P44 signal between bus sockets
* See daisy chain details below
JP23Connect voltage supervisor, U1, to the reset signal

JP 1 to JP22 allow some signals to be isolated between bus sockets. This can be helpful if there are several modules that use these signals for different functions.

Typically the signals will be connected straight through to each bus socket by fitting jumper shunts horizontally, as illustrated to the left.

Alternatively, a daisy chain can be created from pin 39 to 38. This requires a jumper shunt to be fitted in the position illustrated to the left. A second daisy chain can be created from pin 43 to 42.

A daisy chain is created with two pins on each module. One pin is an output signal while the other is an input signal. The jumper connects the output of one module to the input of the next. The illustration below shows the jumper positions required to create a daisy chain between four modules, in bus sockets K1 to K4.

Daisy chains are typically use to create a priority ‘chain’. In the case illustrated above the output is from pin 39 of one module and this is connected to the input pin 38 on the input of module to the right. This creates a priority chain where the modules on the left are a higher priority than modules on the right.

Typical uses for a daisy chain are the Z80 mode 2 interrupt priority, IEI and IEO signals. This is specified as using pins 39 and 38. The second chain, using pins 43 and 42 can be used for a DMA priority chain.

Priority chains require all bus slots in the chain to be occupied by suitable modules. A gap can be left by fitting a pair of jumper shunts horizontally to pass the input and output signals straight through to the bus socket not use the chain signals, rather than being crossed from output to input pins.

The illustration above configures the backplane for a daisy chain where bus socket K3 does not receive a crossed chain signal and thus should not contain a module which is part of the chain. Socket K3 can be empty or can contain a module which does not have connections to pins 39 or 38.

Assembly Guide

Below is the suggested order of assembly. A general guide to assembling circuit boards can be found here.

  • Resistors R1 and R2
    These can be fitted either way around
  • Decoupling capacitors C1 to C12
    These can be fitted either way around
  • Capacitor C14
    This can be fitted either way around
  • Header pins JP23 plus P1
  • Switch SW2
  • Switch SW1
  • Capacitor C13
    This must be fitted the correct way around, as described here
  • Bus socket S1
  • Header pins JP1 to JP22
  • Bus sockets K1 to K12
  • Barrel socket J1
  • Screw terminal J2
  • LED1
    This must be fitted the correct way around, as described here
  • Voltage supervisor U1
    Carefully bend the legs to match the hole spacing on the PCB and ensure the orientation matches the markings on the PCB


  • This product is designed for hobby use and is not suitable for industrial, commercial, or safety-critical applications.
  • The product contains small parts and is not suitable for young children.

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