Casio/Boss Interfacing
Last updated 27 July 97

This page concentrates on the interfaces between Casio/Boss units and a PC computer. For other details look at Victor Wiewiorowski's page at This site is very busy and so sometimes seems unreachable.


Interfaces 1 and 2 use the MAX232/3 chip. These interfaces are slightly more expensive to make than interfaces 3 and 4 but are much more compact.

Interfaces 3 and 4 use the MC14C88 and MC14C89 and are cheaper to construct than interfaces 1 and 2.

The Casio 4300B does not work with interfaces 1 and 2.

Interface 1

Circuit diagram

This interface uses a MAX232 as the main interfacing chip. The MAX232 is a 14 pin DIL package and in addition the circuit also requires a few capacitors and a voltage regulator. The circuit can be made small enough to fit inside a 25 way D-type hood.

Interface 2

Circuit diagram

This interface is a modified version of interface 1 which uses the MAX233 instead of the MAX232. The MAX233 is an 18 pin DIL package and does not require external capacitors. The 18 pin package is 0.2" longer which means it cannot usually fit inside a 25 way D-type hood widthways which can make it harder to fit inside the hood.

Interface 3

Circuit diagram

This interface uses a MC14C88 and MC14C89. These components are sometimes easier to find than a MAX232 and are considerably cheaper. Like the earlier interfaces it it powered completely off the RS232 port.

Interface 4

Circuit diagram

When I built interface 3 I found that the circuit drew too much current from the +ve supply from the RTS line and therefore modified the circuit to run a section off a 9V battery. Since then I have found the problem to be due to the particular DS14C89 that I was using. I already had a nice case for the unit and so I stuck with using interface 4 myself.

You can use interface 4 if in the unlikely event that interface 3 draws too much current from the RTS line.


Ian Laverty has written some excellent shareware windows based software. The software is called Casif/Win and can be obtained from

Ian Laverty who runs IMSL software now has a web page with details about the Casif/Win software. Have a look at

Other Info

The Casio Data Format

Click here to view a text file containing the data format.

Component information

RS232 plug pinouts 78L05 pinouts 2.5mm Jack connections



Ready Made Interfaces

Denis Rouleau offers the following services.

Denis has a web page with more details of how to order the interfaces.

Software & Cables in Spain

There is a Spanish distributer or cables & software. Visit