SC16C752 datasheet(10/47 Pages) PHILIPS

10 / 47 page

Philips Semiconductors

SC16C752

Dual UART with 64-byte FIFO

Product data

Rev. 04 — 20 June 2003

10 of 47

9397 750 11635

6.3.2

Xoff1/2 character is transmitted when the RX FIFO has passed the HALT trigger level

programmed in TCR[3:0].

Xon1/2 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 Xoff1,2/Xon1,2 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. Figure 6 shows an example of software ﬂow control.

6.3.3

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.

UART 1 begins transmission and sends 52 characters, at which point UART2 will

generate an interrupt to its processor to service the RCV FIFO, but assume the

interrupt latency is fairly long. UART1 will continue sending characters until a total of

Fig 6.

Software ﬂow control example.

TRANSMIT FIFO

PARALLEL-TO-SERIAL

SERIAL-TO-PARALLEL

Xon-1 WORD

Xon-2 WORD

Xoff-1 WORD

Xoff-2 WORD

RECEIVE FIFO

PARALLEL-TO-SERIAL

SERIAL-TO-PARALLEL

Xon-1 WORD

Xon-2 WORD

Xoff-1 WORD

Xoff-2 WORD

UART2

UART1

002aaa229

DATA

Xoff–Xon–Xoff

COMPARE

PROGRAMMED

Xon-Xoff

CHARACTERS

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