SC28L194A1BE 查看數據表（PDF） - Philips Electronics

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SC28L194A1BE

Quad UART for 3.3V and 5V supply voltage

Philips Electronics 

Philips Semiconductors

Quad UART for 3.3V and 5V supply voltage

Preliminary specification

SC28L194

Table 1. Interrupt Arbitration Priority

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ Type

B9

B8

B7

B6

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ Receiver w/o error

RxFIFO Byte Count -1

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ Receiver w/ error

RxFIFO Byte Count -1

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ Transmitter

0

TxFIFO Byte Count -1

Change of Break

Programmed Field

0

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ Change of State

Programmed Field

0

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ Xon/Xoff

Programmed Field

0

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ Address Recognition

Programmed Field

0

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ Receiver Watch-dog

RxFIFO Byte Count -1

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ Threshold

Bits 6:0 of Interrupt Control Register

B5

B4

0

0

1

0

0

0

1

1

1

1

1

0

1

As RxFIFO Above

B3

1

1

0

0

0

1

1

Bits 2:0

Channel No

Channel No

Channel No

Channel No

Channel No

Channel No

Channel No

Channel No

000

Note several characteristics of the above table in bits 6:3. These bits

the DSR (Data Set Ready) signal from the modem. In this case its

contain the identification of the bidding source as indicated below:

arbitration value should be high. Once the DSR is recognized then

x001 Receiver without error

its arbitration value could be reduced or turned off.

x101

xx00

0010

0110

0111

0011

Receiver with error

Transmitter

Change of Break

Change of State on I/O Ports

Xon/Xoff Event

Address Recognition

The codes form bits 6:3 drive part of the interrupt vector modification

and the Global Interrupt Type Register. The codes are unique to

each source type and Identify them completely. The channel

numbering progresses from “a” to “d” as the binary numbers 000 to

011 and identify the interrupting channel uniquely. As the channels

arbitrate “d” will have the highest bidding value and “a” the lowest

There is a single arbiter interrupt number that is not associated with

any of the UART channels. It is the “Threshold Value” and is

comprised of 7 bits from the Interrupt Control Register, ICR, and

three zeros in the channel field. It is only when one or more of the

enabled interrupt sources generates a arbitration value larger

than the threshold value that the IRQN will be asserted. When

the threshold bidding value is larger than any other bidding value

then the IRQN will be withdrawn. In this condition, when nothing is

interrupting, the CIR will be loaded with zeros if the IRQN is

asserted or “Update CIR” command is issued. Because the

channels are numbered from 0 to 3 ( A to D) channel 3 will win the

bid when all other parts of the bid are equal.

Note that the transmitter byte count is off-set from that of the

receiver by one bit. This is to give the receiver more authority in the

arbitration since and over-run receiver corrupts the message but an

under-run transmitter is not harmful. This puts some constraints on

how the threshold value is selected. If a threshold is chosen that has

its MSB set to one then a transmitter can never generate an

interrupt! Of course the counter point to this is the desire to set the

interrupt threshold high so interrupts occur only when a maximum or

near maximum number of characters may be transferred.

To give some control over this dilemma control bits have been

provided in the MR0 and MR2 registers of each channel to

individually control when a receiver or transmitter may interrupt. The

use of these bits will prevent a receiver or a transmitter from

entering the arbitration process even though its FIFO fill level is

above that indicated by the threshold value set. The bits in the MR0

and MR2 register are named TxINT (MR0[5:4]) and RxINT

(MR2[3:2])

Watch-Dog Timer

The watch-dog is included in the table above to show that it affects

the arbitration. It does not have an identity of its own. A barking

watch-dog will prevent any other source type from entering the

arbitration process except enabled receivers. The threshold is

effectively set to zero when any watch-dog times out. The receivers

arbitrate among them selves and the one with the highest fill level

will win the process. Note that the receiver wining the bid may not be

the one that caused the watch-dog to bark.

The fields labeled “Programmed Field” are the contents of the

Bidding Control Registers, BCRs, for these sources. Setting these

bits to high values can elevate the interrupt importance of the

sources they represent to values almost as high as a full receiver.

For example a COS event may be very important when it represents

Note: Based on the xx00 coding for the transmitter (as shown

in Table 1 above), a transmitter will not win a bid in the situation

where the Count Field = 0 unless the threshold value is equal to

or less than 0000011. A single empty slot is left in the TxFIFO,

or a single filled slot in the RxFIFO will bid with a byte count

value of zero.

MODES OF OPERATION

Major Modes

Four major modes of operation (normal, auto echo, local loop back

and remote loop back) are provided and are controlled by MR2[7:6].

Three of these may be considered diagnostic. See the MR2 register

description.

The normal mode is the usual mode for data I/O operation. Most

reception and transmission will use the normal mode.

In the auto echo mode, the transmitter automatically re-transmits

any character captured by the channel’s receiver. The receiver 1x

clock is used for the transmitter. This mode returns the received

data back to the sending station one bit time delayed from its

departure. Receiver to host communication is normal. Host to

transmitter communication has no meaning.

In the local loop back mode (used for diagnostic purposes) the

transmitter is internally connected to the receiver input. The

transmitter 1x clock used for the receiver. The RxD input pin is

ignored and the transmitter TxD output pin is held high. This

configuration allows the transmitter to send data to the receiver

without any external parameters to affect the transmission of data.

All status bits, interrupt conditions and processor interface operate

normally. It is recommended that this mode be used when

initially verifying processor to UART interface. The

1998 Sep 21

12

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