FDC37C665GT Datasheet, PDF (86/152 Pages) SMSC Corporation – High-Performance Multi-Mode Parallel Port Super I/O Floppy Disk Controllers

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 as 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
register to the RCVR FIFO. It is reset when
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 register is written to (1
of 16 characters may be 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 be 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
XMITTER are controlled separately, either one
or both can be in the polled mode of operation.
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