Here are the few functionality level understanding of the RS232 transceivers.
1. When the RS232 transceiver enters low power mode, the transmitter is disabled and it shall be in high impedance state. If you are using RS232 transceiver with multiple TX/RX pins, in that case also all the transmitters shall be in high impedance state. This high impedance state feature is very useful when multiple devices are connected.
2. Receiver inputs are always active, they are never in high impedance state. When a RS232 transceiver is in high impedance state, any transition/valid RS232 level on the receiver brings it to the normal operating mode.
3. The present RS232 transceivers have automated power-down modes or the manual power-down modes. Automated power down modes go to a standby mode after few seconds of inactivity on the TX/RX lines. In manual mode, the device need to be set to standby mode using GPIO pins of micro controller connected to FORCEON/FORCEOFF pins of the transceiver.
4. The RS232 devices have pull-down resistor on the RX lines which defines the input impedance of the RS232 transceiver.
5. Most of the RS232 devices have ESD protection built-in on the TX/RX lines.
6. The RS232 transceivers available today have two different supply pins, one for the actual powering of the device and second one a logic supply which defines the logic level at the controller side. The logic level voltage and supply voltage can be different. In some cases, this helps eliminate level translator at the controller side.
7. There are devices classified as true RS232 levels or RS232 levels. True RS232 levels are as per the standard RS232 level specifications and at driver side varies from -5V to +5V and at receiver it varies from -25V to +25V.
8. When the transceiver is rated for specific data rate like for example, 250kbps, then that is the specification for the full-load conditions of 3kohm resistance and 1000pF capacitance. As many times we don't have 1000pF load connected at the output, much higher data rates can be achieved with the given RS232 transceiver.
9. The unused transmitter inputs should never be left open, in a transceiver with multiple TX pins. Unused pins causes higher current than desired.
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