The Casio CFX 9850G connections

This Page describes possibilities to connect your calculator to PC´s or other Casio calculators. The link makes you able to share your programs and data with your friends and to get some nice programs from the depth of the Internet...

I have compiled the Page from two other Webpages (see the links below) and added some more useful comments, because I missed some information when I made the inetrface for myself.

The Casio to Casio Link

The connection between two calculators is very easy to build. You will need the following:

2x 2.5mm stereo plug

2x ferrite ring core (ca. 5 mm high and 10 mm for the inner diameter)

1m wire (for three connections)

On the left image you see my nice drawing of the stereo plug with corresponding signal names for each conact. You have to connect the two jacks as the following:

Plug 1 Plug 2

GND GND

RX TX

TX RX

Before you do this, don´t forget to wind the cable 2 times arround the ferrite ring core (my cable haven´t worked without these). If you use a usual jack be sure that it *really* fits the calculators socket. I had to cut the front edge of the plastic case to make it fit :-). I think your first cable must be ready now...

The Casio to PC link

How you´ve expected, the interface to an usual PC is a little more complicated. It uses a CMOS IC (U1) to invert the logic signals from PC and CASIO. While this it converts also the voltage levels from the +/-12 V from the RS232 to 0...3 V for the calculator. With a direct connection of the interfaces you will damage your CASIO! My circuit uses the RTS pin of the RS232 as voltage source. The IC A1 drops it down to 5 V to drive the logic IC. If power supply is active, the LED D2 will light, usually when you start a transmission. You also have to short some pins of the RS232 to create the right "handshaking" for the CASIO software.
CASIO to PC interface circuit

Component list:

symbol component

R1                10 kOhm
R2                10 kOhm
R3                100 Ohm
R4                1.5 kOhm
C1                10 nF
C2                1 nF
D1                Diode (low voltage rectifying, eg 1N4148)
D2                low current LED yellow or red ( 2mA),
                  if you want a green one ( 4mA) R4 must be around 800 Ohm
A1                MC 78L05 (5V voltage regulator, positive)
U1                CMOS IC    4093 (or any other CMOS NAND gate IC)

RS232 female D-plug         9- pin           25- pin
X1                GND        5                7
X2                RTS        7                4
X3                TX         3                2
X4                RX         2                3
you also have to short:
                             7 to 8           4 to 5
                             6 to 1 and 4     6 to 8 and 20

Casio plug
X5                GND
X6                RX
X7                TX

some wire to connect the PCB with the plugs:
3 and 4 line cable, each 50 ro 70cm long

If you got all the stuff, you can start to assemble it. I used a small prototyping board, but you can make your own printed circuit board, too. The following image may help you to connect the right pins, if you are not familiar with the components. component pin assignments

Now you have to get the right software, to transmitt data to your CASIO. There is an software package, called FX-Interface, which is sold with the original CASIO Interface cable. Additionally there are some public domain programmes in the depth of the net. You should lock for some other CASIO related sites. On the Link Page you will find some of them.

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