When a microcontroller wants to access data in its external memory, it activates an active-LOW output pin called R̅D̅ (read). The data book says that the R̅D̅ pulse typically has a pulse width t_w of 50 ns, a rise time t_r of 15 ns, and a fall time t_f of 10 ns. Draw a scaled drawing of the R̅D̅ pulse.