ST92196A STMicroelectronics, ST92196A Datasheet - Page 53

• Manufacturer Part Number: ST92196A
• Description: 8/16-bit Mcu For Tv Applications With Up To 96k Rom, On-screen-display And 1 Or 2 Data Slicers
• Manufacturer: STMicroelectronics

3.7 TOP LEVEL INTERRUPT
The Top Level Interrupt channel can be assigned
either to the external pin NMI or to the Timer/
Watchdog according to the status of the control bit
EIVR.TLIS (R246.2, Page 0). If this bit is high (the
reset condition) the source is the external pin NMI.
If it is low, the source is the Timer/ Watchdog End
Of Count. When the source is the NMI external
pin, the control bit EIVR.TLTEV (R246.3; Page 0)
selects between the rising (if set) or falling (if reset)
edge generating the interrupt request. When the
selected event occurs, the CICR.TLIP bit (R230.6)
is set. Depending on the mask situation, a Top
Level Interrupt request may be generated. Two
kinds of masks are available, a Maskable mask
and a Non-Maskable mask. The first mask is the
CICR.TLI bit (R230.5): it can be set or cleared to
enable or disable respectively the Top Level Inter-
rupt request. If it is enabled, the global Enable In-
terrupt bit, CICR.IEN (R230.4) must also be ena-
bled in order to allow a Top Level Request.
The second mask NICR.TLNM (R247.7) is a set-
only mask. Once set, it enables the Top Level In-
terrupt request independently of the value of
CICR.IEN and it cannot be cleared by the pro-
gram. Only the processor RESET cycle can clear
this bit. This does not prevent the user from ignor-
ing some sources due to a change in TLIS.
The Top Level Interrupt Service Routine cannot be
interrupted by any other interrupt or DMA request,
in any arbitration mode, not even by a subsequent
Top Level Interrupt request.
Figure 24. Top Level Interrupt Structure
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n
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INTERRUPTS
NMI
TLNM
IEN
WATCHDOG ENABLE
TLI
WATCHDOG TIMER
END OF COUNT
WDEN
TLTEV
OR
MUX
TLIS
Warning. The interrupt machine cycle of the Top
Level Interrupt does not clear the CICR.IEN bit,
and the corresponding iret does not set it. Fur-
thermore the TLI never modifies the CPL bits and
the NICR register.
3.8 ON-CHIP PERIPHERAL INTERRUPTS
The general structure of the peripheral interrupt
unit is described here, however each on-chip pe-
ripheral has its own specific interrupt unit contain-
ing one or more interrupt channels, or DMA chan-
nels. Please refer to the specific peripheral chap-
ter for the description of its interrupt features and
control registers.
The on-chip peripheral interrupt channels provide
the following control bits:
– Interrupt Pending bit (IP). Set by hardware
– Interrupt Mask bit (IM). If IM = “0”, no interrupt
– Priority Level (PRL, 3 bits). These bits define
– Interrupt Vector Register (IVR, up to 7 bits).
when the Trigger Event occurs. Can be set/
cleared by software to generate/cancel pending
interrupts and give the status for Interrupt polling.
request is generated. If IM =“1” an interrupt re-
quest is generated whenever IP = “1” and
CICR.IEN = “1”.
the current priority level, PRL=0: the highest pri-
ority, PRL=7: the lowest priority (the interrupt
cannot be acknowledged)
The IVR points to the vector table which itself
contains the interrupt routine start address.
TLIP
PENDING
MASK
TOP LEVEL
INTERRUPT
CORE
RESET
REQUEST
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