SB16C1054_Data Sheet_EN
SB16C1054
QUAD UART WITH 256-BYTE FIFO
FEBRUARY 2009 REV 1.0
5
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7.4 Interrupt Status Register (ISR, Page 0)
The UART provides multiple levels of prioritized interrupts to minimize software work load.
ISR provides the source of interrupt in a prioritized manner.
Table 10 shows ISR[7:0] bit settings.
Table 10: Interrupt Status Register Description
Bit Symbol Description
7 ISR[7] FCR[0]/256 TX FIFO Empty.
When 256-byte FIFO mode is disabled (default).
Mirror the content of FCR[0].
When 256-byte FIFO mode is enabled.
0 : 256-byte TX FIFO is full.
1 : 256-byte TX FIFO is not full.
When TCR is ‘00h’, there are two situations of TX FIFO full and TX FIFO empty. If 256 TX
empty bit is ‘1’, it means TX FIFO is empty and if ‘0’, it means 256 bytes character is fully
stored in TX FIFO.
6 ISR[6] FCR[0]/256 RX FIFO Full.
When 256-byte FIFO mode is disabled (default).
Mirror the content of FCR[0].
When 256-byte FIFO mode is enabled.
0 : 256-byte RX FIFO is not full.
1 : 256-byte RX FIFO is full.
When RCR is ‘00h’, there are two situations of RX FIFO full and RX FIFO empty. If 256 RX
empty bit is ‘1’, it means 256 bytes character is fully stored in RX FIFO and if ‘0’, it means
RX FIFO is empty.
Table 10: Interrupt Status Register Description…continued
Bit Interrupt Priority List and Reset Functions
5:0 Priority
Interrupt Type Interrupt Source Interrupt Reset Control
00
_
0001
― None None ―
00
_
0110
1 Receiver Line Status OE, PE, FE, BI Reading the LSR.
00
_
0100
2 Receive Data Available
Receiver data available, reaches
trigger level.
Reading the RBR or RCR
falls below trigger level.
00
_
1100
2 Character Timeout Indi-
cation
At least one data is in RX FIFO and
there are no more data in FIFO during
four character time.
Reading the RBR.
00
_
0010
3 Transmit Holding
Register Empty
When THR is empty or TCR passes
above trigger level (FIFO enable).
Reading the ISR or write
data on THR.
00
_
0000
4 Modem Status CTS#, DSR#, DCD#, RI# Reading the MSR.
01
_
0000
5 Receive Xoff or Special
Character
Detection of a Xoff or special character.
Reading the ISR.
10
_
0000
6 RTS#, CTS# Status
during Auto RTS/CTS
flow control
RTS# pin or CTS# pin change state
from ‘0’ to ‘1’.
Reading the ISR.