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过去,当电话机台数超过二十台时,电缆对数必然大大增多。而这种利用微型信息处理机及数字式传输技术,且实现了开关动作电子化的电子式键
In the past, when the number of telephones exceeded twenty, the number of cables inevitably increased significantly. The use of micro-information processors and digital transmission technology, and the realization of the switch action electronic electronic keys