OX16PCI952-TQAG OXFORD [Oxford Semiconductor], OX16PCI952-TQAG Datasheet - Page 40

• Manufacturer Part Number: OX16PCI952-TQAG
• Description: Integrated High Performance Dual UARTs, Parallel Port and 5.0v PCI interface
• Manufacturer: OXFORD [Oxford Semiconductor]

7.6.2
The source of the highest priority interrupt pending is
indicated by the contents of the Interrupt Status Register
‘ISR’. There are nine sources of interrupt at six levels of
priority (1 is the highest) as shown in Table 19.
Note1:
Note2:
UART is in Enhanced mode.
Note3:
when FIFO size is 16 and ‘1’ when FIFO size is 128. In all other modes it
is permanently set to 0
7.6.3
Level 1:
Receiver status error interrupt (ISR[5:0]=’000110’):
Normal (non-9-bit) mode:
This interrupt is active whenever any of LSR[1], LSR[2],
LSR[3] or LSR[4] are set. These flags are cleared following
a read of the LSR. This interrupt is masked with IER[2].
9-bit mode:
This interrupt is active whenever any of LSR[1], LSR[2],
LSR[3] or LSR[4] are set. The receiver error interrupt due
to LSR[1], LSR[3] and LSR[4] is masked with IER[3]. The
‘address-bit’ received interrupt is masked with NMR[1]. The
software driver can differentiate between receiver status
error and received address-bit (9
examining LSR[1] and LSR[7]. In 9-bit mode LSR[7] is only
set when LSR[3] or LSR[4] is set and it is not affected by
LSR[2] (i.e. 9
DS-0028 Jul 05
Level
-
1
2a
2b
3
4
5
6
OXFORD SEMICONDUCTOR LTD.
2
2
Table 19: Interrupt Status Identification Codes
Interrupt Status Register ‘ISR’
ISR[0] indicates whether any interrupts are pending.
Interrupts of priority levels 5 and 6 cannot occur unless the
ISR[5] is only used in 650 & 950 modes. In 750 mode, it is ‘0’
Interrupt Description
Interrupt source
No interrupt pending
Receiver status error or
Address-bit detected in 9-bit mode
Receiver data available
Receiver time-out
Transmitter THR empty
Modem status change
In-band flow control XOFF or
Special character (XOFF2) or
Special character 1, 2, 3 or 4 or
bit 9 set in 9-bit mode
CTS or RTS change of state
th
data bit).
1
th
data bit) interrupt by
ISR[5:0]
see note 3
000001
000110
000100
001100
000010
000000
010000
100000
External-Free Release
Level 2a:
Receiver data available interrupt (ISR[5:0]=’000100’):
This interrupt is active whenever the receiver FIFO level is
above the interrupt trigger level.
Level 2b:
Receiver time-out interrupt (ISR[5:0]=’001100’):
A receiver time-out event, which may cause an interrupt,
will occur when all of the following conditions are true:
•
•
•
•
Reading the first data item in RHR clears this interrupt.
Level 3:
Transmitter empty interrupt (ISR[5:0]=’000010’):
This interrupt is set when the transmit FIFO level falls
below the trigger level. It is cleared on an ISR read of a
level 3 interrupt or by writing more data to the THR so that
the trigger level is exceeded. Note that when 16C950 mode
trigger levels are enabled (ACR[5]=1) and the transmitter
trigger level of zero is selected (TTL=0x00), a transmitter
empty interrupt will only be asserted when both the
transmitter FIFO and transmitter shift register are empty
and the SOUT line has returned to idle marking state.
Level 4:
Modem change interrupt (ISR[5:0]=’000000’):
This interrupt is set by a modem change flag (MSR[0],
MSR[1], MSR[2] or MSR[3]) becoming active due to
changes in the input modem lines. This interrupt is cleared
following a read of the MSR.
Level 5:
Receiver in-band flow control (XOFF) detect interrupt,
Receiver special character (XOFF2) detect interrupt,
Receiver special character 1, 2, 3 or 4 interrupt or
9
A level 5 interrupt can only occur in Enhanced-mode when
any of the following conditions are met:
•
•
•
It is cleared on an ISR read of a level 5 interrupt.
th
Bit set interrupt in 9-bit mode (ISR[5:0]=’010000’):
The UART is in a FIFO mode
There is data in the RHR.
There has been no read of the RHR for a period of
time greater than the time-out period.
There has been no new data written into the RHR for
a period of time greater than the time-out period. The
time-out period is four times the character period
(including start and stop bits) measured from the
centre of the first stop bit of the last data item
received.
A valid XOFF character is received while in-band flow
control is enabled.
A received character matches XOFF2 while special
character detection is enabled, i.e. EFR[5]=1.
A received character matches special character 1, 2, 3
or 4 in 9-bit mode (see section 7.11.9).
OX16PCI952
Page 40