The uPD72042B is designed to allow for an external protection resistor, whereas the uPD6708 is not.
Therefore, when using the uPD6708 and uPD72042B together, use the following recommended protection resistance and terminating resistance values.
• Terminating resistor: 120 Ω (dual ended) or 60 Ω (single ended)
• Protection resistor for uPD72042B: 180 Ω
• Protection resistor for uPD6708: 0 Ω