SC16C752B datasheet(11/47 Pages) PHILIPS

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Philips Semiconductors

SC16C752B

5 V, 3.3 V and 2.5 V dual UART, 5 Mbit/s (max.), with 64-byte FIFOs

Product data

Rev. 03 — 14 December 2004

11 of 47

9397 750 14443

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

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 RX FIFO that the level drops to 32. UART2 will now

send a 0D to UART1, informing UART1 to resume transmission.

Fig 7.

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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