TL16CP754C Datasheet, PDF (11/49 Pages) Texas Instruments – QUAD UARTS WITH 64-BYTE FIFO

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UART 1
Transmit
FIFO
TL16CP754C, TL16CM754C, TL16C754C
SLLS644E – DECEMBER 2007 – REVISED MAY 2010
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-1 Word
Compare
Programmed
Xon- Xoff
Characters
Xoff-2 Word
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 assumes the interrupt latency is fairly long. UART1 continues sending
characters until a total of 60 characters have been sent. At this time UART2 will transmit a 0F to UART1,
informing UART1 to halt transmission. UART1 will likely send the 61st 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.
Reset
Table 2 summarizes the state of outputs after reset.
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