Samsung KS57C2308 manual Vectored Interrupts, Software-Generated Interrupts, Multiple Interrupts

INTERRUPTS KS57C2308/P2308/C2316/P2316

Vectored Interrupts

Interrupt requests may be processed as vectored interrupts in hardware, or they can be generated by program software. A vectored interrupt is generated when the following flags and register settings, corresponding to the specific interrupt (INTn) are set to logic one:

—Interrupt enable flag (IEx)

—Interrupt master enable flag (IME)

—Interrupt request flag (IRQx)

—Interrupt status flags (IS0, IS1)

—Interrupt priority register (IPR)

If all conditions are satisfied for the execution of a requested service routine, the start address of the interrupt is loaded into the program counter and the program starts executing the service routine from this address.

EMB and ERB flags for RAM memory banks and registers are stored in the vector address area of the ROM during interrupt service routines. The flags are stored at the beginning of the program with the VENT instruction. The initial flag values determine the vectors for resets and interrupts. Enable flag values are saved during the main routine, as well as during service routines. Any changes that are made to enable flag values during a service routine are not stored in the vector address.

When an interrupt occurs, the EMB and ERB flag values before the interrupt is initiated are saved along with the program status word (PSW), and the enable flag values for the interrupt is fetched from the respective vector address. Then, if necessary, you can modify the enable flags during the interrupt service routine. When the interrupt service routine is returned to the main routine by the IRET instruction, the original values saved in the stack are restored and the main program continues program execution with these values.

Software-Generated Interrupts

To generate an interrupt request from software, the program manipulates the appropriate IRQx flag. When the interrupt request flag value is set, it is retained until all other conditions for the vectored interrupt have been met, and the service routine can be initiated.

Multiple Interrupts

By manipulating the two interrupt status flags (IS0 and IS1), you can control service routine initialization and thereby process multiple interrupts simultaneously.

If more than four interrupts are being processed at one time, you can avoid possible loss of working register data by using the PUSH RR instruction to save register contents to the stack before the service routines are executed in the same register bank. When the routines have executed successfully, you can restore the register contents from the stack to working memory using the POP instruction.

Power-Down Mode Release

An interrupt (with the exception of INT0) can be used to release power-down mode (stop or idle). Interrupts for power-down mode release are initiated by setting the corresponding interrupt enable flag. Even if the IME flag is cleared to zero, power-down mode will be released by an interrupt request signal when the interrupt enable flag has been set. In such cases, the interrupt routine will not be executed since IME = "0".

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