SC28L201 datasheet(62/110 Pages) NXP

62 / 110 page

9397 750 13138

Product data sheet

Rev. 01 — 31 October 2005

62 of 110

Philips Semiconductors

SC28L201

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

8.3.4 Xon/Xoff Interrupt Status Register (XISR)

Reading this register clears XISR[7:4].

Table 36:

XISR - Xon/Xoff Interrupt Status Register (address 0x44) bit description

Bit

Symbol

Description

7:6

Received X Character Status.

00 = none

01 = Xoff received

10 = Xon received

11 = both received

This ﬁeld can be read to determine if the receiver has encountered an Xon

or Xoff character in the incoming data stream. These bits are maintained

until a read of the XISR. The ﬁeld is updated by X character reception

regardless of the state of MR3[7] and MR3[3:2] or IMR[4]. The ﬁeld can

therefore be used as a character detector for the bit patterns stored in the

Xon and Xoff Character Registers.

5:4

Automatic X Character transmission status.

00 = none

01 = Xon transmitted

10 = Xoff transmitted

11 = both transmitted

This ﬁeld indicates the last ﬂow control character sent in the Auto Receiver

ﬂow control mode. If Auto Receiver mode has not been enabled, this ﬁeld

will always read 00. It will likewise reset to ‘00’ if MR0[3] is reset. If the Auto

Receiver mode is exited while this ﬁeld reads ‘10’, it is the user’s

responsibility to transmit an Xon, when appropriate.

3:2

TXD ﬂow status. TXD condition of the automatic ﬂow control status.

This ﬁeld tracks the transmitter’s ﬂow status as follows:

00 = normal transmission. Transmitter is not affected by Xon or Xoff.

01 = TXD halt pending. After the current character ﬁnishes the transmitter

will stop. The status will then change to ‘11’.

10 = re-enabled. The transmitter had been halted and has been

re-started. It is sending (or is prepared to send) data characters.

After a read of the XISR, it will return to ‘normal’ status.

11 = ﬂow halted. The Transmitter is stopped due to an Xoff character

being received from its associated receiver. The transmitter is ‘ﬂow

controlled’.

1:0

TXD X Character Status.

00 = normal TXD data.

01 = Idle wait for FIFO data. The character is waiting for a data character

to transfer from the TxFIFO. This condition will only occur for a bit time

after an Xon or Xoff character transmission unless the TxFIFO is empty

10 = Xoff is pending. A command to send an Xoff character is pending.

11 = Xon is pending. A command to send an Xon character is pending.

Conditions ‘10’ and ‘11’ will not exist for more than a character time.

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