The searial bus is useless until initial setup. It doesn´t know Plug and Play. Every device reacts diferently to the signals. To controll a searial bus you can use terminal programs like for example Putty
Control using UART
Uart is short for Universal Asynchronous Receiver Transmitter. Using UART, the hardware orientates itself around the so called start bit. The start bit tells the devices, that a transmission is to be expected. After transmission there is a stop bit which officially ends the data transfer of that package,
Controlling the bus manualy
A a programmer can write his own skript to make the bus do what he wants.
To do that he or she needs to know what pin does what:
| Pin 9 Poles | Signal | ||
| 1 | DCD | Data Carier Detect | |
| 2 | RxD | Receive Dat | |
| 3 | TxD | Transmit Data | |
| 4 | DTR | Data Terminal Ready | |
| 5 | SG/GND | Ground | |
| 6 | DSR | Data Set Ready | |
| 7 | RTS | Request to Send, | |
| 8 | CTS | Clear to send | |
| 9 | RI | Ring Indicator | |
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| Pin 25 Poles | Signal | ||
| 1 | PE | Protective Earth | |
| 2 | TxD | Transmit Data | |
| 3 | RxD | Receive Data | |
| 4 | RTS | Request to Send | |
| 5 | CTS | Clear to Send | |
| 6 | DSR | Data Set Ready | |
| 7 | SG /GND | Ground | |
| 8 | DCD | Data Carrier Detect | |
| 9 | Test | ||
| 10 | Test | ||
| 11 | NC | ||
| 12 | SCD | Secondary DCD | |
| 13 | SCTS | Secondary CTS | |
| 14 | STxD | Secondary TxD | |
| 15 | TxC | Transmit Clock | |
Conection usin a Null Modem
The Null modem is used to connect two devices without using a modem. Its like a crossover cable. It has a pretty basic principle: TxD goes to RxD and vice versa.
There are multiple ways of realising a Null modem:
| Description Bus 1 | DCD, DSR | RxD | TxD | DTR | GND | RTS | CTS |
| Pin | 1 and 6 | 2 | 3 | 4 | 5 | 7 | 8 |
| Pin | 4 | 3 | 2 | 1 and 6 | 5 | 8 | 7 |
| Description Bus 2 | DTR | TxD | RxD | DCD, DSR | GND | CTS | RTS |
Using this, a handshake is possible.
The handshake makes sure both devices know if they have to listen or to send.
The way without handshake is much easier
| Description Bus 1 | DCD | RxD | TxD | DTR | GND | DSR,RI | RTS,CTS |
| Pin | 1 | 2 | 3 | 4 | 5 | 6 und 9 | 7 und 8 |
| Pin | 1 | 3 | 2 | 4 | 5 | 6 und 9 | 7 und 8 |
| Description Bus 2 | DCD | TxD | RxD | DTR | GND | DSR,RI | RTS, CTS |
On pin 6 and 9 and on pin 7 and 8 there is a bridge to negate the harwareflowcontroll. You use that bridge if your devices cant handle it.