Datasheet

UART 1
Parallel to Serial
Serial to Parallel
Xon-1 Word
Xon-2 Word
Xoff-1 Word
Xoff-1 Word
Transmit
FIFO
Serial to Parallel
Parallel to Serial
Xon-1 Word
Xoff-1 Word
Xoff-2 Word
Receive
FIFO
Data
Xoff − Xon − Xoff
Compare
Programmed
Xon−Xoff
Characters
UART 2
Xon-2 Word
TL16C752B-EP
www.ti.com SGLS153B –FEBRUARY 2003–REVISED DECEMBER 2007
Figure 4. Software Flow Control Example
Software Flow Control Example
Assumptions: UART1 is transmitting a large text file to UART2. Both UARTs are using software flow control with
single character Xoff (0F) and Xon (0D) tokens. Both have Xoff threshold (TCR [3:0]=F) set to 60 and Xon
threshold (TCR[7:4]=8) set to 32. Both have the interrupt receive threshold (TLR[7:4]=D) set to 52.
UART1 begins transmission and sends 52 characters, at which point UART2 generates an interrupt to its
processor to service the RCV FIFO, but assume the interrupt latency is fairly long. UART1 continues sending
characters until a total of 60 characters have been sent. At this time UART2 transmits a 0F to UART1, informing
UART1 to halt transmission. UART1 likely sends the 61
st
character, while UART2 is sending the Xoff character.
UART2 is serviced and the processor reads enough data out of the RCV FIFO that the level drops to 32. UART2
now sends a 0D to UART1, informing UART1 to resume transmission.
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