User's Manual

UART S3C2450X RISC MICROPROCESSOR
15-4
2.1.3 Auto Flow Control (AFC)
UART 0, UART 1 and UART 2 support auto flow control with nRTS and nCTS signals. In AFC, nCTS signals
control the operation of the transmitter, and nRTS depends on the condition of the receiver.
The UART's transmitter transfers the data in FIFO only when nCTS signals are activated(Low) (In AFC, nCTS
means that other UART's FIFO is ready to receive data or not).
Before the UART receives data, nRTS signal has to be activated(Low) when its receive FIFO has a spare space
more than 32-byte(FIFO contains less than 32-byte). And nRTS signal has to be inactivated(High) when its
receive FIFO has a spare under 32-byte(FIFO contains equal or more than 32-byte) in case of RTS trigger level is
32byte. (In AFC, nRTS means that its own receive FIFO is ready to receive data or not).
UART A
TxD
nCTS
UART B
RxD
nRTS
Transmission Case in UART A
UART A
RxD
nRTS
UART B
TxD
nCTS
Reception Case in UART A
Figure 15-2. UART AFC Interface
NOTE
UART 3 does not support AFC function, because the S3C2450 has no nRTS 3 and nCTS 3.
S3C2450’s AFC does not support the RS-232C interface.
Table 15-1. Example of nRTS signal change by FIFO Spare size
(In case of Reception Case in UART A)
RX side TX side
FIFO
Contains
FIFO Spare
Space
nRTS
Signal
nRTS
Meaning
nCTS
Signal
nCTS
Meaning
33 byte 31 byte High Not ready to receive High Don’t send data to RX side
32 byte
32 byte High Not ready to receive High Don’t send data to RX side
31 byte
33 byte Low Ready to Receive
Low Send data to RX side
30 byte
34 byte Low Ready to Receive
Low Send data to RX side