Hardware Flow Control

Versal ACAP Technical Reference Manual (AM011)

Document ID
AM011
Release Date
2022-04-26
Revision
1.4 English

The hardware flow control feature is fully selectable. This feature enables the control of the serial data flow by using the UARTX_CTS_b output and UARTX_RTS_b input signals.

The following figure shows communication between two devices using the hardware flow control.

Figure 1. Hardware Flow Control Between Two Similar Devices

When the RTS flow control is enabled, UARTX_RTS_b is asserted until the receive FIFO is filled up to the programmed watermark level. When the CTS flow control is enabled, the transmitter can only transmit data when UARTX_CTS_b is asserted.

The hardware flow control is selectable using the [RTSEn] and [CTSEn] bits in the Control register, UART CTRL . The following table lists the bit settings used to enable RTS and CTS flow control both simultaneously and independently.

Table 1. Control Bits to Enable and Disable Hardware Flow Control
CTSEn RTSEn Description
1 1 Both RTS and CTS flow control enabled
1 0 Only CTS flow control enabled
0 1 Only RTS flow control enabled
0 0 Both RTS and CTS flow control disabled
Note: When RTS flow control is enabled, the software cannot use the [RTSEn] bit in the Control register,UART CTRL to control the status of UARTX_RTS_b.