RS232 - UART

lead in rs232 is a relatively legacy wired protocol that appeared on desktop terminals and it remained available until recent history when it slowly started to be phased on on notebooks the native interface is still available on a desktop personal computer physical connection the basic connection for an rs232 or serial connection has three wires transmit, usually indicated as tx receive, usually indicated as rx ground, usually indicated as gnd the rs232 protocol is not natively powered, and neither of the devices would normally power the other they would share a common ground as this ensures that the rs signal is sent and received in relation to the same ground when connecting the pic, the communication lines swap over so the mcu tx connects to the modules rx and vice versa specifications voltage levels rs232 also used as ground & 5v level binary 0 works with voltages up to +5v to +15vdc it is called as ‘on’ or spacing (high voltage level) whereas binary 1 works with voltages up to 5v to 15vdc it is called as ‘off’ or marking (low voltage level) received signal voltage level binary 0 works on the received signal voltages up to +3v to +13 vdc & binary 1 works with voltages up to 3v to 13 vdc line impedances the impedance of wires is up to 3 ohms to 7 ohms & the maximum cable length are 15 meters, but new maximum length in terms of capacitance per unit length operation voltage the operation voltage will be 250v ac max current rating the current rating will be 3 amps max dielectric withstanding voltage 1000 vac min slew rate the rate of change of signal levels is termed as slew rate with its slew rate is up to 30 v/microsecond and the maximum bitrate will be 20 implementation the physical implementation offers a number of cable configurations connector pinouts there are two common cable connectors, which are wired up depending on the use the two connectors are interchangeable, and an adapter can be made up for better connection lead out a max232 would have provided the voltage signal levels in the past where the 12v | 1 and the +12v | 0 however, with the disappearance of the 9 pin | 25 pin adapter from your standard pc, we use the 4 pin usb type a connector the pc based driver in conjunction with the usb uart simulates the various standard coms signals so the mcu if waiting for the dtr signal, will receive one via the chg340