ox16cf950 ETC-unknow, ox16cf950 Datasheet - Page 33

• Manufacturer Part Number: ox16cf950
• Description: Cost Asynchronous Card
• Manufacturer: ETC-unknow

6.6.2
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 tabulated below:
Note1:
Note2:
Note3:
6.6.3
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
Level 2a:
Receiver data available interrupt (ISR[5:0]=’000100’):
Level
OXFORD SEMICONDUCTOR LTD.
2a
2b
5
6
1
3
4
-
2
2
Table 31: Interrupt Status Identification Codes
ISR[0] indicates whether any interrupts are pending.
Interrupts of priority levels 5 and 6 cannot occur unless
the UART is in Enhanced mode.
ISR[5] is only used in 650 & 950 modes. In 750 mode, it
is ‘0’ when FIFO size is 16 and ‘1’ when FIFO size is
128. In all other modes it is permanently set to ‘0’.
Interrupt Status Register ‘ISR’
Interrupt Description
Address-bit detected in 9-bit mode
Special character 1, 2, 3 or 4 or
th
Special character (XOFF2) or
In-band flow control XOFF or
CTS or RTS change of state
data bit).
Receiver status error or
Receiver data available
Transmitter THR empty
Modem status change
No interrupt pending
bit 9 set in 9-bit mode
Receiver time-out
Interrupt source
th
data bit) interrupt by
1
ISR[5:0]
see note 3
000001
000110
000100
001100
000010
000000
010000
100000
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 l e vel 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 950 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:
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 o f the RHR for a period of
time greater than the time-out period.
There has been no new data received and 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.
A received character matches special character 1, 2, 3
or 4 in 9-bit mode (see sect i on 6.11.9).
OXCF950 DATA SHEET V1.1
Page 33