CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (Clock Timer)

EIT0: 32 Hz interrupt mask register (FFE6H•D0)EIT1: 8 Hz interrupt mask register (FFE6H•D1)EIT2: 2 Hz interrupt mask register (FFE6H•D2)EIT3: 1 Hz interrupt mask register (FFE6H•D3)

These registers are used to select whether to mask the clock timer interrupt.

When "1" is written: Enabled

When "0" is written: Masked

Reading: Valid

The interrupt mask registers (EIT0, EIT1, EIT2, EIT3) are used to select whether to mask the interrupt to the separate frequencies (32 Hz, 8 Hz, 2 Hz, 1 Hz).

At initial reset, these registers are set to "0".

IT0: 32 Hz interrupt factor flag (FFF6H•D0)IT1: 8 Hz interrupt factor flag (FFF6H•D1)IT2: 2 Hz interrupt factor flag (FFF6H•D2)IT3: 1 Hz interrupt factor flag (FFF6H•D3)

These flags indicate the status of the clock timer interrupt.

When "1" is read: Interrupt has occurred

When "0" is read: Interrupt has not occurred

When "1" is written: Flag is reset

When "0" is written: Invalid

The interrupt factor flags (IT0, IT1, IT2, IT3) correspond to the clock timer interrupts of the respective frequencies (32 Hz, 8 Hz, 2 Hz, 1 Hz). The software can judge from these flags whether there is a clock timer interrupt. However, even if the interrupt is masked, the flags are set to "1" at the falling edge of the signal.

These flags are reset to "0" by writing "1" to them.

After an interrupt occurs, the same interrupt will occur again if the interrupt enabled state (I flag = "1") is set or the RETI instruction is executed unless the interrupt factor flag is reset. Therefore, be sure to reset (write "1" to) the interrupt factor flag in the interrupt service routine before shifting to the interrupt enabled state.

At initial reset, these flags are set to "0".

4.8.5 Programming notes

(1)Be sure to read timer data in the order of low-order data (TM0–TM3) then high-order data (TM4– TM7).

(2)After an interrupt occurs, the same interrupt will occur again if the interrupt enabled state (I flag = "1") is set or the RETI instruction is executed unless the interrupt factor flag is reset. Therefore, be sure to reset (write "1" to) the interrupt factor flag in the interrupt service routine before shifting to the interrupt enabled state.

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S1C63558 TECHNICAL MANUAL