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© Koninklijke Philips Electronics N.V. 2005. All rights reserved.

Product data sheet

Rev. 01 — 9 February 2005

17 of 51

Philips Semiconductors

SC16C554B/554DB

5 V, 3.3 V and 2.5 V quad UART, 5 Mbit/s (max.) with 16-byte FIFOs

6.4.3 Enabling autoflow control and auto-CTS

Autoflow control is enabled by setting MCR[5] and MCR[1].

6.4.4 Auto-CTS and auto-RTS functional timing

The receiver FIFO trigger level can be set to 1, 4, 8, or 14 bytes. These are described in

Figure 9 and Figure 10.

Table 7:

Enabling autoflow control and auto-CTS

MCR[5]

MCR[1]

Selection

1

1

auto RTS and CTS

1

0

auto CTS

0

X

disable

(1) When CTS is LOW, the transmitter keeps sending serial data out.

(2) If CTS goes HIGH before the middle of the last stop bit of the current byte, the transmitter finishes sending the current byte,

but is does not send the next byte.

(3) When CTS goes from HIGH to LOW, the transmitter begins sending data again.

Fig 8.

CTS functional timing waveforms

Start

bits 0 to 7

Stop

TX

CTS

002aaa049

Start

bits 0 to 7

Stop

Start

bits 0 to 7

Stop

(1) N = RCV FIFO trigger level (1, 4, or 8 bytes).

(2) The two blocks in dashed lines cover the case where an additional byte is sent as described in the preceding auto-RTS

section.

Fig 9.

RTS functional timing waveforms, RCV FIFO trigger level = 1, 4, or 8 bytes

Start

byte N

Start

byte N + 1

Start

byte

Stop

Stop

Stop

RX

RTS

IOR

(RD RBR)

N

N + 1

12

002aaa050