Tying a flow control line (like RTS or CTS) to ground is done to trick a device into thinking it is always cleared and ready to transmit data, bypassing hardware handshaking.
Why it’s done
- Bypass Flow Control: Many legacy devices, PLCs, or software drivers refuse to send or receive data unless they see an active signal on their CTS (Clear to Send) or RTS (Request to Send) pins.
- Enable 3-Wire Operation: If you only have a basic 3-wire cable (TX, RX, Ground) but the connected device expects 5-wire hardware handshaking, jumping or grounding the pin fools the receiver into a permanent "ready" state.
Possible issues
- Buffer Overflow: Without actual handshaking, the transmitting device will keep throwing data even if the receiving device's buffer is full, which leads to data corruption or dropped packets.
- Device Lockup: On certain microcontrollers or wireless modules, pulling the wrong control pin to ground permanently can leave the device unresponsive or crashed if it expects a toggled voltage logic level rather than a static ground.