CTS, or Clear to Send, is a crucial signal in serial communication, particularly within the RS232 standard, used for hardware flow control.
Understanding CTS in RS232
RTS/CTS flow control is a mechanism that utilizes the RTS (Request to Send) and CTS (Clear to Send) pins on the RS232 connector. These lines enable the receiver and transmitter to communicate their status to each other, preventing data loss.
How CTS Works:
- Role: CTS is an input signal to the transmitting device.
- Function: The receiving device asserts (activates) the CTS signal to indicate that it's ready to receive data. If the CTS signal is not asserted, the transmitting device should wait before sending data.
- Purpose: CTS ensures that the transmitter doesn't overwhelm the receiver with data, preventing buffer overflows and data loss.
RTS/CTS Flow Control in Action:
| Signal | Direction | Description |
|---|---|---|
| RTS | Output | Request to Send: Asserted by the transmitter to indicate its readiness to send. |
| CTS | Input | Clear to Send: Asserted by the receiver to grant permission to send data. |
- The transmitting device asserts its RTS line, signaling its intent to send data.
- The receiving device checks its buffer status.
- If the receiver is ready, it asserts its CTS line, informing the transmitter that it can proceed with sending data.
- If the receiver is busy or its buffer is full, it de-asserts the CTS line, signaling the transmitter to pause.
- The transmitter monitors the CTS line and only sends data when CTS is asserted.
Benefits of Using CTS:
- Prevents Data Loss: Ensures that data is not sent when the receiver is not ready.
- Hardware-Based: Provides reliable flow control managed directly by the hardware.
- Standard Protocol: Part of the widely used RS232 standard.
