w83977tf Winbond Electronics Corp America, w83977tf Datasheet - Page 55

• Manufacturer Part Number: w83977tf
• Description: Winbond I/o
• Manufacturer: Winbond Electronics Corp America

3.2.6 Interrupt Status Register (ISR) (Read only)
This register reflects the UART interrupt status, which is encoded by different interrupt sources into 3
bits.
Bit 7, 6: These two bits are set to a logical 1 when UFR bit 0 = 1.
Bit 5, 4: These two bits are always logic 0.
Bit 3: In 16450 mode, this bit is 0. In 16550 mode, both bit 3 and 2 are set to a logical 1 when a time-out
Bit 2, 1: These two bits identify the priority level of the pending interrupt, as shown in the table below.
Bit 0: This bit is a logical 1 if there is no interrupt pending. If one of the interrupt sources has occurred,
TABLE 3-4 INTERRUPT CONTROL FUNCTION
** Bit 3 of ISR is enabled when bit 0 of UFR is logical 1.
Bit
3
0
0
0
1
0
0
interrupt is pending.
this bit will be set to a logical 0.
Bit
2
0
1
1
1
0
0
ISR
Bit
1
0
1
0
0
1
0
Bit
0
1
0
0
0
0
0
7
Interrupt
priority
First
Second
Second
Third
Fourth
-
6
Interrupt Type
UART Receive
Status
RBR Data Ready
FIFO Data Timeout
TBR Empty
Handshake status
0
5
4
0
-
3
INTERRUPT SET AND FUNCTION
2
Interrupt Source
No Interrupt pending
1. OER = 1
3. NSER = 1 4. SBD = 1
1. RBR data ready
2. FIFO interrupt active level
Data present in RX FIFO for 4
characters period of time since last
access of RX FIFO.
TBR empty
1. TCTS = 1
3. FERI = 1
- 47 -
reached
1
0
2. PBER =1
4. TDCD = 1
2. TDSR = 1
0 if interrupt pending
Interrupt Status bit 0
Interrupt Status bit 1
Interrupt Status bit 2
FIFOs enabled
FIFOs enabled
Publication Release Date: March 1998
W83977TF
PRELIMINARY
Clear Interrupt
Read USR
1. Read RBR
2. Read RBR until FIFO
data under active level
Read RBR
1. Write data into TBR
2. Read ISR (if priority is
Read HSR
third)
Revision 0.62
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