RS-232
RS 232 is the protocol we will use for communication here we will discuss the aspect when we will use it
Why we use RS 232 Protocol??
Why we use RS 232 Protocol??
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The RS-232 standard defines the voltage levels that correspond to logical one and logical zero levels. Valid signals are plus or minus 3 to 15 volts. The range near zero volts is not a valid RS-232 level; logic one is defined as a negative voltage, the signal condition is called marking, and has the functional significance of OFF. Logic zero is positive, the signal condition is spacing, and has the function ON. The standard specifies a maximum open-circuit voltage of 25 volts; signal levels of ±5 V,±10 V,±12 V, and ±15 V are all commonly seen depending on the power supplies available within a device
DB9 Connector
1 DSR
2 RxD
3 TxD
4 DTR
5 Grnd
6 DSR
7 RTS
8 CTS
9 RI
Mainly we use pin 2,3 and 5 for configuration to establish connection
Transmitted Data (TxD):
Data sent from DTE to DCE.
Received Data (RxD) :
Data sent from DCE to DTE.
Request To Send (RTS) :
Asserted (set to 0) by DTE to prepare DCE to receive data. This may require action on the part of the DCE, e.g. transmitting a carrier or reversing the direction
Clear To Send (CTS):
Asserted by DCE to acknowledge RTS and allow DTE to transmit.
Data Terminal Ready (DTR):
Asserted by DTE to indicate that it is ready to be connected. If the DCE is a modem, this may "wake up" the modem, bringing it out of a power saving mode. This behaviour is seen quite often in modern PSTN and GSM modems. When this signal is de-asserted, the modem may return to its standby mode, immediately hanging up any calls in progress.
Data Set Ready (DSR) :
Asserted by DCE to indicate an active connection. If DCE is not a modem (e.g. a null modem cable or other equipment), this signal should be permanently asserted (set to 0), possibly by a jumper to another signal.
Data Carrier Detect (DCD) :
Asserted by DCE when a connection has been established with remote equipment.
Ring Indicator (RI) :
Asserted by DCE when it detects a ring signal from the telephone line