atmega32u4-16mu ATMEL Corporation, atmega32u4-16mu Datasheet - Page 223

• Manufacturer Part Number: atmega32u4-16mu
• Description: Atmega32u4 8-bit Avr Microcontroller With 32k Bytes Of Isp Flash And Usb Controller
• Manufacturer: ATMEL Corporation

19.9.1
19.9.2
7766A–AVR–03/08
Receiver Flow Control
Transmission Flow Control
The reception flow can be controlled by hardware using the RTS pin. The aim of the flow control
is to inform the external transmitter when the internal receive Fifo is full. Thus the transmitter can
stop sending characters. RTS usage and so associated flow control is enabled using RTSEN bit
in UCSRnD.
Figure 5. shows a reception example.
Figure 5. Reception Flow Control Waveform Example
Figure 6. RTS behavior
RTS will rise at 2/3 of the last received stop bit if the receive fifo is full.
To ensure reliable transmissions, even after a RTS rise, an extra-data can still be received and
stored in the Receive Shift Register.
The transmission flow can be controlled by hardware using the CTS pin controlled by the exter-
nal receiver. The aim of the flow control is to stop transmission when the receiver is full of data
(CTS = 1). CTS usage and so associated flow control is enabled using CTSEN bit in UCSRnD.
The CTS pin is sampled at each CPU write and at the middle of the last stop bit that is cur-
rently being sent.
Figure 7. CTS behavior
Read from CPU
Write from CPU
RXD
RTS
TXD
CTS
sample
Start
Start
Index
FIFO
RXD
RTS
Byte0
Byte0
Stop
Stop
0
sample
C1 C2
1
Start
Start
2
CPU Read
1
Byte1
Byte1
C3
0
Stop
Stop
1
sample
1 additional byte may be sent
if the transmitter misses the RTS trig
ATmega32U4
Start
Start
Byte2
Byte2
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