Introduction to CASIO's proprietary protocols
Communication among CASIO calculators has drastically evolved throughout the years; this section is there to describe the different used protocols, and where you can find them (date & time).
I don’t know anything about communication among CASIO calculators until a 3-pin connector was added to them, so you’ll have to look for another source of information about these.
When the 3-pin connector was introduced among CASIO calculators, around the 1990s, they used a protocol that I name “CASIO-Link”, or usually simply “CAS”. This protocol has had a few variants over the years:
CAS40: the original CAS protocol, which didn’t allow much;
CAS50: a more evolved CAS protocol, used since around 1995;
CAS100: a special form of the CAS protocol for the AlgebraFX family (around 1998-2002).
The overall packet flow is the same (with some tiny exceptions), only the header and data format varies a little. The CAS40 protocol variant is too simple to be upwards compatible, and the CAS100 cannot be compatible as it doesn’t use the same default serial settings than the others (all protocols except this one are used at 9600 bauds, and this one is used at 19200 bauds).
The fx-9860G series (starting in 2004 with the release of the fx-9860G, named “Graph 85” in France) is special, as everything, including the OS, protocol and software, has been rebuilt from bottom up. Although they can still communicate with a CAS50-speaking calculator, they use their own protocol, named “Protocol 7.00” or sometimes “P7” by the community. This protocol can be used on USB and 3-pin mediums, for transferring files, screen streaming, and OS updating.
Then the fx-CG series (Prizm, Graph 90+E) came in 2011, and introduced the usage of SCSI over USB cables (although Protocol 7.00/CAS50 is still used on 3-pin, for compatibility with other calculator models). Screenstreaming can be executed both as a Protocol 7.00 extension, and SCSI extended commands.