SC2200 datasheet(119/433 Pages) NSC

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SuperI/O Module (Continued)

4.5.2.9

Interrupt Handling

The RTC has a single Interrupt Request line which handles

the following three interrupt conditions:

• Periodic interrupt.

• Alarm interrupt.

• Update end interrupt.

The interrupts are generated if the respective enable bits in

the CRB register are set prior to an interrupt event occur-

rence. Reading the CRC register clears all interrupt flags.

Thus, when multiple interrupts are enabled, the interrupt

service routine should first read and store the CRC regis-

ter, and then deal with all pending interrupts by referring to

this stored status.

If an interrupt is not serviced before a second occurrence

of the same interrupt condition, the second interrupt event

is lost. Figure 4-12 illustrates the interrupt timing in the

RTC.

Figure 4-12. Interrupt/Status Timing

4.5.2.10 Battery-Backed RAMs and Registers

The RTC has two battery-backed RAMs and 17 registers,

used by the logical units themselves. Battery-backup power

enables information retention during system power down.

The RAMs are:

• Standard RAM

• Extended RAM

The memory maps and register content of the RAMs is

provided in Section 4.5.4 "RTC General-Purpose RAM

Map" on page 124.

The first 14 bytes and 3 programmable bytes of the Stan-

dard RAM are overlaid by time, alarm data and control reg-

isters. The remaining 111 bytes are general-purpose

memory.

Registers with reserved bits should be written using the

read-modify-write method.

All register locations within the device are accessed by the

RTC Index and Data registers (at base address and base

address+1). The Index register points to the register loca-

tion being accessed, and the Data register contains the

data to be transferred to or from the location. An additional

128bytes of battery-backedRAM (alsocalledExtended

RAM) maybeaccessedvia asecondpair ofIndex and

Data registers.

Access to the two RAMs may be locked. For details see

Table 4-7 on page 108.

244

µs

Bit 7

Bit 4

Bit 6

Bit 5

of CRA

of CRC

P/2

30.5

µs

Flags (and IRQ) are reset at the conclusion of CRC read or by

reset.

A = Update In Progress bit high before update occurs = 244

µs

B = Periodic interrupt to update = Period (periodic int) / 2 +

244

µs

C = Update to Alarm Interrupt = 30.5

µs

P = Period is programmed by RS[3:0] of CRA

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