SC28L201 datasheet(33/110 Pages) NXP

33 / 110 page

9397 750 13138

Product data sheet

Rev. 01 — 31 October 2005

33 of 110

Philips Semiconductors

SC28L201

3.3 V, 5 V UART, 3.125 Mbit/s, with 256-byte FIFO

Remark: Reading the XISR Clears the status bits associated with the recognition.

The characters of the recognition system are fully programmable. The Xon/Xoff

characters will be set to the standard characters if the hardware or software reset is used.

The character recognition circuits are basically designed to provide general-purpose

character recognition. Additional control logic has been added to allow for Xon/Xoff ﬂow

control and for recognition of the address character in the multi-drop or Wake-up mode.

This logic also allows for the generation of interrupts in either the general-purpose

recognition mode or the speciﬁc conditions mentioned above.

The generality of the above provides a modicum of compatibility to BOP (Bit Oriented

Protocol) where the generation and detection of ‘ﬂags’ is required. Parts of usually

synchronous BOP protocols (HDLC in particular) are beginning to show up in

asynchronous formats.

7.4.9.1

Character stripping

The MR0[7:6] register provides for stripping (meaning not set to the RxFIFO) the

characters used for character recognition. Recall that the character recognition may be

conditioned to control several aspects of the communication. However this system is ﬁrst a

character recognition system. The status of the various states of this system is reported in

the XISR and ISR registers. The character stripping of this system allows for the removal

of the speciﬁed control characters from the data stream: two for the Xon /Xoff and one for

the wake-up. Via control in the MR0[7:6] register these characters may be discarded

(stripped) from the data stream when the recognition system ‘sees’ them or they may be

sent on the RxFIFO. Whether they are stripped or not the recognition system will process

them according to the action requested; ﬂow control, wake-up, interrupt generation, and

so on. Care should be exercised in programming the stripping option if noisy

environments are encountered. If a normal character were corrupted to an Xoff character

the transmitter would be stopped. If that character were now stripped from the FIFO stack,

then that stripping action would make it difﬁcult to determine the cause of transmitter

stopping.

When character stripping is invoked and a recognition character is received that has an

error bit set that character is sent to the RxFIFO even though character stripping is

active.

7.4.10 Flow control (Xon/Xoff)

This section describes in-band ﬂow control or Xon/Xoff signaling. For the RTS/CTS

hardware (out-of-band) control see MR1[7] and MR2[4] descriptions.

The ﬂow control is accomplished via the character recognition system giving recognition

information to the ﬂow control processor. Xon and Xoff are special characters used by a

receiver to start and stop the remote transmitter that is sending it data. Several modes of

manual and automatic ﬂow control are available by programming mode control.

7.4.10.1

Mode control

Xon/Xoff mode control is accomplished via the MR3[3:2].

00 — Xon/Xoff processing disabled. The host will control Rx, Tx.

01 — Auto Tx control. Tx is stopped/started when Xoff/Xon is received.

10 — Auto Rx control. Receiver commands Tx to send Xoff at trigger level.

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