TL16C752CI-Q1_16 Datasheet, PDF (21/57 Pages) Texas Instruments – Dual UART

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UART 1
Transmit
FIFO
TL16C752CI-Q1
SLLSEQ9A – OCTOBER 2015 – REVISED FEBRUARY 2016
UART 2
Receive
FIFO
Parallel to Serial
Serial to Parallel
Data
Xoff − Xon − Xoff
Serial to Parallel
Parallel to Serial
Xon-1 Word
Xon-1 Word
Xon-2 Word
Xon-2 Word
Xoff-1 Word
Xoff-1 Word
Xoff-2 Word
Compare
Programmed
Xon −Xoff
Characters
Xoff-2 Word
Figure 19. Software Flow Control Example
8.3.1.6 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 assumes 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.
Now, 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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