IRCC datasheet(48/79 Pages) SMSC

48 / 79 page

Effect Of The Reset on Register File

The Reset Function Table (Table 30) details the

effect of the Reset input on each of the registers of

the Serial Port.

FIFO INTERRUPT MODE OPERATION

When the RCVR FIFO and receiver interrupts are

enabled (FCR bit 0 = "1", IER bit 0 = "1"), RCVR

interrupts occur as follows:

A. The receive data available interrupt will be

issued when the FIFO has reached its

programmed trigger level; it is cleared as

soon

the

FIFO

drops

below

its

programmed trigger level.

B. The IIR receive data available indication also

occurs when the FIFO trigger level is reached.

It is cleared when the FIFO drops below the

trigger level.

C. The receiver line status interrupt (IIR=06H),

has higher priority than the received data

available (IIR=04H) interrupt.

D. The data ready bit (LSR bit 0)is set as soon

as a character is transferred from the shift

the FIFO is empty.

When RCVR FIFO and receiver interrupts are

enabled, RCVR FIFO timeout interrupts occur as

follows:

A. A FIFO timeout interrupt occurs if all the

following conditions exist:

−

at least one character is in the FIFO

−

The

most

recent

serial

character

received was longer than 4 continuous

character times ago. (If 2 stop bits are

programmed, the second one is included

in this time delay.)

−

The most recent CPU read of the FIFO

was longer than 4 continuous character

times ago.

−

This will cause a maximum character

received to interrupt issued delay of 160

msec at 300 BAUD with a 12 bit

character.

B. Character times are calculated by using the

RCLK input for a clock signal (this makes the

delay proportional to the baudrate).

C. When a timeout interrupt has occurred it is

cleared and the timer reset when the CPU

reads one character from the RCVR FIFO.

D. When a timeout interrupt has not occurred the

timeout timer is reset after a new character is

received or after the CPU reads the RCVR

FIFO.

When the XMIT FIFO and transmitter interrupts

are enabled (FCR bit 0 = "1", IER bit 1 = "1"),

XMIT interrupts occur as follows:

A. The transmitter holding register interrupt (02H)

occurs when the XMIT FIFO is empty; it is

cleared as soon as the transmitter holding

written to the XMIT FIFO while servicing this

interrupt) or the IIR is read.

B. The transmitter FIFO empty indications will be

delayed 1 character time minus the last stop

bit time whenever the following occurs:

THRE=1 and there have not been at least two

bytes at the same time in the transmitte FIFO

since the last THRE=1.

The transmitter

interrupt

after

changing

FCR0

will

immediate, if it is enabled.

Character timeout and RCVR FIFO trigger level

interrupts have the sme priority as the current

received data available interrupt; XMIT FIFO

empty has the same priority as the current

transmitter holding register empty interrupt.

FIFO POLLED MODE OPERATION

With FCR bit 0 = "1" resetting IER bits 0, 1, 2 or 3

or all to zero puts the UART in the FIFO Polled

Mode of operation.

Since the RCVR and are

controlled separately, either one or both can be in

the polled mode of operation.

IRCC 数据表(PDF) 48 Page - SMSC Corporation

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