Datasheet

349
32133D–11/2011
UC3D
20.6.3.12 Hardware Handshaking
The USART features an out-of-band hardware handshaking flow control mechanism, imple-
mentable by connecting the RTS and CTS pins with the remote device, as shown in Figure 20-
14.
Figure 20-14. Connection with a Remote Device for Hardware Handshaking
Writing 0x2 to the MR.MODE field configures the USART to operate in this mode. The receiver
will drive its RTS pin high when disabled or when the Reception Buffer Full bit (CSR.RXBUFF) is
set by the Buffer Full signal from the Peripheral DMA controller. If the receivers RTS pin is high,
the transmitters CTS pin will also be high and only the active character transactions will be com-
pleted. Allocating a new buffer to the DMA controller by clearing RXBUFF, will drive the RTS pin
low, allowing the transmitter to resume transmission. Detected level changes on the CTS pin
can trigger interrupts, and are reported by the CTS Input Change bit in the Channel Status Reg-
ister (CSR.CTSIC).
Figure 20-15 illustrates receiver functionality, and Figure 20-16 illustrates transmitter
functionality.
Figure 20-15. Receiver Behavior when Operating with Hardware Handshaking
Figure 20-16. Transmitter Behavior when Operating with Hardware Handshaking
Figure 20-17.
USART
TXD
CTS
Remote
Device
RXD
TXDRXD
RTS
RTS
CTS
RTS
R
XBUFF
Write
CR
RXEN = 1
RXD
RXDIS = 1
CTS
TXD