|Casio Graphic Calculators|
The Casio fx-9750G Plus
Why Link Up
Linking Two Calculators
Linking To A PC
The Casio fx-9750G Plus:
In recent years schools have suggested, or even requested that Year 13 (7th form) students use graphic calculators. Not unusually, everyone seems to have purchased the same "low cost" model from Casio. This model is the fx-9750G Plus. For those who aren't so good with model numbers, it looks like this:
These calculators have a communications port built into them for copying data and programs from one calculator to another or from a calculator to a PC. The plug can be found on the bottom edge of the unit, between the (-) and EXE keys. (not clearly shown above) A large number of older Casio graphic calculators also have this port and should work with the equipment and software described here, but don't hold me to it, I've only had a chance to test them on the fx-9750G Plus.
A very similar model for those with deeper pockets is the CFG-9850GB Plus, which is essentially the same piece with a three color (not full color) display. I have found this model to be compatible with the fx-9750G Plus in all respects concerning the data communications features which this article addresses.
Why Link Up:
For the more mathematically inclined there's a few reasons the data communications features of most Casio graphic calculators can be useful. By linking two calculators together you can share list data, copy programs and a few other less useful things. For example, you can have one person enter a large collection of data into a list file and quickly distribute it to any number of calculators. Copying a list with say two hundred elements takes only a few seconds.
A link to a PC is useful for three things. Backing up data, (paranoid about your batteries?), saving hours (yes, hours) when writing programs for the calculator and downloading games to play during the more boring classes. Sure, you can write programs into the calculator using the built in keypad but almost all the functions, keywords and statements are accessed only through menus which appear on the bottom of the display. These menus only display six items a time, five in most cases, meaning you'll spend most your time pressing shift and wondering what menu the command you need is in. It takes a few hours to create anything of decent size. Programs can be written on your PC at home in a fraction of the time and downloaded into the calculator for execution.
If you don't use the programmable feature of these calculators, it is unlikely you will find a PC link very useful.
Linking Two Calculators:
Connecting two calculators together is very simple and easy, and costs very little. All that is needed in the way of parts is a phono 2.5mm stereo plug for each end of the cable, (smaller versions of a standard earphone plug) and a short length of three conductor wire. (Twin core shielded audio is best, just make sure it will fit in the plug back-shell)
The wiring is simple; connect the base of the 2.5mm plugs together (signal ground) and form a crossover between the middle and tip, as shown below.
While the cable I made was only about a foot long, I don't see why longer cables won't work. Lengthy cables in a classroom just aren't a good idea, unless you want to trip the teacher up and loose the cable. A short cable for stealing your neighbours statistics data can have it's uses though....
Copying data is also quite simple. On both calculators select LINK from the Main Menu, (middle of bottom row on the fx-9750G) then Receive (F2) on the unit you're copying to, which will then proceed to wait for data. On the unit sending data, select Transmit (F1) then Select (F1) and use F1 to flag data (program files, list files.... etc) for copying. Press F6 to start the transfer. The selected data should now appear in the appropriate places on the receiving calculator. Easy....
Somebody mentioned to me that some fancier calculators have infrared transceivers built in so that you can do what a link cable would allow without any extra hardware. (these calculators have "Infra-Red" emblazoned on the front, and usually aren't admitted into exams)
I have received a number of requests over the last year or so for information about an infrared link, so I have created a page which discusses infrared communication. Please refer to the Infrared Serial Communications article.
Linking To A PC:
For those who have reason, linking your calculator to a PC is a little more involved. The PC software transmits and receives data using the same asynchronous data format and protocol as the calculators use to talk to each other, but the serial port logic voltage is not compatible. For this reason, do not connect the serial port directly to your calculator as the RS-232 voltages on the serial port will likely damage the interface circuitry.
I have used a line driver to convert the voltage levels. There are other methods but line drivers tend to be smaller and cheaper. A schematic for my version of the required adapter is below.
While the 78L05 regulator, 1N4004 diode and 22µF capacitor can easily fit into the D-SUB back-shell, the MAX232 and 2.2µF capacitors (which have to be as close to the MAX232 as possible) will probably need some sort of housing.
The circuit itself isn't actually that complicated. When a application opens a serial port to send or receive data, the DTR line (pin 4 of the COM port) is driven high. This signal is feed into a small (TO-92 package) voltage regulator which provides 5V for the MAX232 line driver as long as DTR is high. When the port is not in use, DTR will be anywhere between 0V and -25V (depending on the PC) which is why a diode has been included to protect the regulator from this reverse potential, which would likely damage it.
Below is a few images of the PC link cable.
The inside of the serial port connector containing the 5V regulator system.
The guts of the in-line box containing the MAX232 line driver.
To use the PC cable you need a small software package to communicate with the calculator and edit programs and data. This software is provided free by Casio, and can be downloaded from here last time I looked. (please tell me if this link doesn't work)
The software has almost nil system requirements, and will even run on Windows 3.x. I won't be posting any screen shots on this site as I don't own the software, but I'll make a few useful notes:
Finally, I should mention that the software has been reported to have some problems under Windows NT. I have quite successfully run it under Windows 2000 Professional (SP4) and Windows XP Home Edition, but others have reported problems. The technical support crew at Casio claim that Windows NT (which includes 2K and XP) is "out of operational support range" and that no updates are available. There are no known problems with Windows 3.x and Windows 9x.
That's all, enjoy!
If you have any comments or questions please don't hesitate to contact me.
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