- 易迪拓培训,专注于微波、射频、天线设计工程师的培养
手机通讯接口 （二） RS-232标准voltage level
录入：edatop.com 点击：
Voltage Levels
在RS-232-C中任何一条信号线的电压均为负逻辑关系。即：逻 辑“1”，-5— -15V；逻辑“0” +5— +15V 。噪声容限为2V。即 要求接收器能识别低至+3V的信号作为逻辑“0”，高到-3V的信号 作为逻辑“1”
The standard specifies a maximum open-circuit voltage of 25 volts; signal levels of ±5V, ±10V, ±12V, and ±15V are all commonly seen depending on the power supplies available within a device.
Circuits driving an RS-232-compatible interface must be able to withstand indefinite short circuit to ground or to any voltage level up to 25 volts. The slew rate is also controlled.
Mark and space are terms carried over from teletypes. The native mode of communication for a teletype is a simple series DC circuit that is interrupted, much as a rotary dial interrupts a telephone signal. The marking condition is when the circuit is closed; the spacing condition is when the circuit is open.
The start of a character is signaled by a space. The stop bits are marking. When the line is broken, a teletype cycles continuously but prints nothing because it is receiving all zeros, the ASCII NUL character.
