SC16C754B NXP Semiconductors, SC16C754B Datasheet - Page 13

• Manufacturer Part Number: SC16C754B
• Description: 5 V - 3.3 V and 2.5 V quad UART - 5 Mbit/s (max.)
• Manufacturer: NXP Semiconductors

NXP Semiconductors
SC16C754B_4
Product data sheet
6.3.3.1 Assumptions
6.3.2 TX
6.3.3 Software flow control example
Xoff1/Xoff2 character is transmitted when the RX FIFO has passed the halt trigger level
programmed in TCR[3:0].
Xon1/Xon2 character is transmitted when the RX FIFO reaches the resume trigger level
programmed in TCR[7:4].
The transmission of Xoff/Xon(s) follows the exact same protocol as transmission of an
ordinary byte from the FIFO. This means that even if the word length is set to be 5, 6, or 7
characters, then the 5, 6, or 7 least significant bits of Xoff1/Xoff2 and Xon1/Xon2 will be
transmitted. (Note that the transmission of 5, 6, or 7 bits of a character is seldom done, but
this functionality is included to maintain compatibility with earlier designs.)
It is assumed that software flow control and hardware flow control will never be enabled
simultaneously.
UART1 is transmitting a large text file to UART2. Both UARTs are using software flow
control with single character Xoff (0Fh) and Xon (0Dh) 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.
Fig 8.
Software flow control example
SERIAL-TO-PARALLEL
PARALLEL-TO-SERIAL
Figure 8
TRANSMIT FIFO
Xon1 WORD
Xon2 WORD
Xoff1 WORD
Xoff2 WORD
5 V, 3.3 V and 2.5 V quad UART, 5 Mbit/s (max.) with 64-byte FIFOs
UART1
Rev. 04 — 6 October 2008
shows an example of software flow control.
Xoff–Xon–Xoff
programmed
characters
compare
Xon-Xoff
data
SERIAL-TO-PARALLEL
PARALLEL-TO-SERIAL
RECEIVE FIFO
Xon2 WORD
Xon1 WORD
Xoff1 WORD
Xoff2 WORD
SC16C754B
UART2
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