s3c72m9 Samsung Semiconductor, Inc., s3c72m9 Datasheet - Page 217

• Manufacturer Part Number: s3c72m9
• Description: The S3c72m5/s3c72m7/s3c72m9 Single-chip Cmos Microcontroller Has Been Designed For High Performance Using Samsung S
• Manufacturer: Samsung Semiconductor, Inc.

S3C72M5/C72M7/C72M9/P72M9 (Preliminary Spec)
MULTIPLE INTERRUPTS
The interrupt controller can service multiple interrupts in two ways: as two-level interrupts, where either all interrupt
requests or only those of highest priority are serviced, or as multi-level interrupts, when the interrupt service routine
for a lower-priority request is accepted during the execution of a higher priority routine.
Two-Level Interrupt Handling
Two-level interrupt handling is the standard method for processing multiple interrupts. When the IS1 and IS0 bits of
the PSW (FB0H.3 and FB0H.2, respectively) are both logic zero, program execution mode is normal and all interrupt
requests are serviced (see Figure 7-3).
Whenever an interrupt request is accepted, IS1 and IS0 are incremented by one ("0"
values are stored in the stack along with the other PSW bits. After the interrupt routine has been serviced, the
modified IS1 and IS0 values are automatically restored from the stack by an IRET instruction.
IS0 and IS1 can be manipulated directly by 1-bit write instructions, regardless of the current value of the enable
memory bank flag (EMB). Before you can modify an interrupt service flag, however, you must first disable interrupt
processing with a DI instruction.
When IS1 = "0" and IS0 = "1", all interrupt service routines are inhibited except for the highest priority interrupt
currently defined by the interrupt priority register (IPR).
INT Disable
INT Enable
High Level
Generated
Interrupt
Set IPR
Low or
Normal Program
Processing
(Status 0)
Figure 7-3. Two-Level Interrupt Handling
High Level
Generated
Interrupt
Interrupt Processing
High or Low Level
(Status 1)
High Level Interrupt
Processing
(Status 2)
"1" or "1"
"0"), and the
INTERRUPTS
7-5