# Hardware Constants Configure your device with the appropriate parity and flow-control options. ## Topics ### Control Bits [`#define PD_RS232_S_DTR`](/documentation/SerialDriverKit/PD_RS232_S_DTR) The data-terminal-ready signal. [`#define PD_RS232_S_DSR`](/documentation/SerialDriverKit/PD_RS232_S_DSR) The data-set-ready signal. [`#define PD_RS232_S_RTS`](/documentation/SerialDriverKit/PD_RS232_S_RTS) The request-to-send signal. [`#define PD_RS232_S_CTS`](/documentation/SerialDriverKit/PD_RS232_S_CTS) The clear-to-send signal. [`#define PD_RS232_S_RXO`](/documentation/SerialDriverKit/PD_RS232_S_RXO) The receive-data signal. [`#define PD_RS232_S_TXO`](/documentation/SerialDriverKit/PD_RS232_S_TXO) The transmit-data signal. [`#define PD_RS232_S_DCD`](/documentation/SerialDriverKit/PD_RS232_S_DCD) The data-carrier-detect signal. ### Parity Options [`#define PD_RS232_PARITY_DEFAULT`](/documentation/SerialDriverKit/PD_RS232_PARITY_DEFAULT) The default parity setting. [`#define PD_RS232_PARITY_NONE`](/documentation/SerialDriverKit/PD_RS232_PARITY_NONE) No parity bit. [`#define PD_RS232_PARITY_ODD`](/documentation/SerialDriverKit/PD_RS232_PARITY_ODD) An odd parity bit. [`#define PD_RS232_PARITY_EVEN`](/documentation/SerialDriverKit/PD_RS232_PARITY_EVEN) An even parity bit. [`#define PD_RS232_PARITY_MARK`](/documentation/SerialDriverKit/PD_RS232_PARITY_MARK) The mark state. [`#define PD_RS232_PARITY_SPACE`](/documentation/SerialDriverKit/PD_RS232_PARITY_SPACE) The space state. [`#define PD_RS232_PARITY_ANY`](/documentation/SerialDriverKit/PD_RS232_PARITY_ANY) Discard the parity bit. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)