SC28L201 datasheet(35/110 Pages) NXP

35 / 110 page

9397 750 13138

Product data sheet

Rev. 01 — 31 October 2005

35 of 110

Philips Semiconductors

SC28L201

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

7.4.10.5

Receiver mode

Since the receiving FIFO resources in the UART are limited, some means of controlling a

remote transmitter is desirable in order to lessen the probability of receiver overrun. The

UART provides two methods of controlling the data ﬂow. There is a hardware-assisted

means of accomplishing control, the so-called out-of-band ﬂow control, and an in-band

ﬂow control method.

The out-of-band ﬂow control is implemented through the CTSN-RTSN signaling via the

I/O ports. The operation of these hardware handshake signals is described in the receiver

and transmitter discussions.

In-band ﬂow control is a protocol for controlling a remote transmitter by embedding special

characters within the message stream, itself. Two characters, Xon and Xoff, which do not

represent normal printable character take on ﬂow control deﬁnitions when the Xon/Xoff

capability is enabled. Flow control characters received may be used to gate the channel

transmitter on and off. This activity is referred to as Auto-transmitter mode. To protect the

channel receiver from overrun, ﬁxed ﬁll levels (hardware set at 240 characters) of the

RxFIFO may be employed to automatically insert Xon/Xoff characters in the transmitters

data stream. This mode of operation is referred to as Auto-receiver mode. Commands

issued by the host CPU via the CR can simulate all these conditions.

7.4.10.6

Auto-receive and transmit (most efﬁcient)

This is a combination of both modes.

Remark: Xon/Xoff characters: The Xon/Xoff character with errors will be accepted as

valid. The user has the option sending or not sending these characters to the FIFO. Error

bits associated with Xon/Xoff will be stored normally to the receiver FIFO.

The channel’s transmitter may be programmed to automatically transmit an Xoff character

without host CPU intervention when the RxFIFO ﬁll level exceeds a ﬁxed limit (240). In this

mode it will transmit an Xon character when the RxFIFO level drops below a second ﬁxed

limit (16). A character from the TxFIFO that has been loaded into the TXD shift register

will continue to transmit. Character(s) in the TxFIFO that have not been loaded to the

transmitter shift register are unaffected by the Xon or Xoff transmission. They will be

transmitted after the Xon/Xoff activity concludes.

If the ﬁll level condition that initiates Xon activity negates before the ﬂow control character

can begin transmission, the transmission of the ﬂow control character will not occur.

Hardware keeps track of Xoff characters sent that are not rescinded by an Xon. This logic

is reset by writing MR3[3:2] to ‘00’. If the user drops out of Auto-receiver mode while the

XISR shows Xoff as the last character sent, the Xon/Xoff logic would not automatically

send the negating Xon.

The disable CRTX command (of the Command Register, 0x18) can be used to cleanly

terminate any pending CRTX commands.

Remark: In no case will an Xon/Xoff character transmission be aborted. Once the

character is loaded into the TX Shift Register, transmission continues until completion or a

chip reset or transmitter reset is encountered. The kill CRTX command has no effect in

either of the Auto modes.

SC28L201 датащи(PDF) 35 Page - NXP Semiconductors

SC28L201 датащи(HTML) 35 Page - NXP Semiconductors

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

датащи скачать

ссылки URL