in a technical side, the cable sb-87 is based on a us patent 5504864, where the technology was previously used in the casio's diary models. the cable was designed to shift the voltage from 6 volts at the calculator's end to 12 volts at the pc's rs-232 end. the chip max232 or max233 by maxim integrated was a core component used to level-shift the voltages between the rs-232 and ttl standards. the sb-88 cable was later developed to embed a usb port into the cable.