ST18-AU1 STMICROELECTRONICS [STMicroelectronics], ST18-AU1 Datasheet - Page 36

• Manufacturer Part Number: ST18-AU1
• Description: SIX-CHANNEL DOLBY AC3/MPEG2 AUDIO DECODER
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

ST18-AU1
The current priority levels available are shown below.
One interrupt request is acknowledged whenever its priority level (coded in the IPR register)
is higher than the current priority level. In this case, the current priority level becomes the
interrupt priority level and the previous current priority level is pushed onto the stack and
displayed as stack priority level (SPL)1.
The process is repeated over a range of four interrupt requests and the four previous current
stack priority levels are displayed on SPL1, SPL2, SPL3 and SPL4. If less than four interrupts
are pushed onto the stack, the unused SPL words are set to ‘000’. At the end of the interrupt
routine, the priority levels are popped from the stack.
The empty stack (ES) flag is used to indicate whether the stack is used or not. The ISP word
of the ISP register indicates the depth of the stack (see below).
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Bit
CPL
ES
SPL1
SPL2
SPL3
SPL4
Function
Current priority level (-1, 0, 1, 2 or 3) (default is 011)
Empty stack flag
3-bit 1st stacked priority level
3-bit 2nd stacked priority level
3-bit 3rd stacked priority level
3-bit 4th stacked priority level
Priority level
Reserved
0: stack is used
1: stack is not used (default)
- 1
0
1
2
3
100 - 110
Coding
111
000
001
010
011
Acceptable IT level priority
0,1,2,3
1,2,3
2,3
3