RS232 for Sharp packet computer

Programming pocket computers is normally a tricky job, owing to the small keys and the small memory. The pocket computers from Sharp, which can be programmed in BASIC, have an Interface that can be connected to a special cassette interface. The signals at that interface are very similar to those of an RS232 Interface, but they are inverted and have different logic levels. It would, of course, be tremendous if the pocket computer could be linked to larger computer via this interface, because the writting, changing and storing of the software could then be done much more conveniently.