As defined by the SMPTE 240 standard, the pulse will start at the zero volts (specified black level) and first transitions negative, to -300 mV (+/- 6 mV).

• 在SMPTE240标准中，脉冲以零伏电压（即黑电平）开始，然后负向跳变为-300mV(+/-6mV)。