Epson RTC-72421 A, RTC-72421 B, RTC-72423, RTC-72423 A MASK, 0 or, Open, Page, MQ - 162, ITRPT/STND, IRQ FLAG bit, STD.P pin output, *STD.P pin output, (1) MASK bit (D0), (4) 30-secondADJ bit (D3)

RTC - 72421 / 72423

*STD.P pin output

IRQ FLAG bit 0 1 0 1

Interrupt generation (in synchronization with count incrementation)

Writing of 0 IRQ FLAG bit.

The output levels of the STD.P pin are low (down) and open circuit (up).

Note: If the STD.P pin output remains low as set, subsequently generated interrupts are ignored. In order to prevent interrupts from being overlooked, write 0 to the IRQ FLAG bit before the next interrupt is generated, to return the STD.P pin to high.

iii. Initial setting of IRQ FLAG bit

If the fixed-period interrupt mode is not used, set the IRQ FLAG bit to 1. If the fixed-period interrupt mode is used, set the IRQ FLAG bit to 0.

(4) 30-second ADJ bit (D3)

The 30-seconds ADJ bit provides a 30-seconds correction (by which term is meant a rounding to the nearest whole minute) when 1 is written to it. The 30-seconds correction takes a maximum of 76.3 ∝ s to perform, and after the correction the 30- seconds ADJ bit is automatically returned to 0. This operation also clears the sub-second bits of the internal counter down to the 1/256-seconds counter. During the 30-seconds correction, access to the counter registers at addresses 0 to C is inhibited, so monitor the 30-seconds ADJ bit to check that this bit has returned to 0, before starting subsequent processing. If no access is made to the RTC for 76.3 ∝ s or more after 1 is written to the 30-seconds ADJ bit, there is no need to check the 30- seconds ADJ bit again.

i. Operation of 30-seconds ADJ bit

Writing 1 to the 30-seconds ADJ bit performs a 30-second correction. This 30-seconds correction changes the seconds and minutes digits as shown below. If the minutes digits have been incremented, an upward carry is propagated.

Status of seconds digits before correction	Status of seconds digits after correction
Up to 29 seconds	00 seconds. No carry to the minutes digits.
30 to 59 seconds	0 seconds. Carry to the minutes digits.

Example: The correction caused by the 30-seconds ADJ bit sets the time within the RTC to 00:00:00 if it was within the range of 00:00:00 to 00:00:29, or to 00:01:00 if it was within the range of 00:00:30 to 00:00:59.

ii. Access inhibited after 30-seconds correction

For 76.3 ∝ s after 1 is written to the 30-seconds ADJ bit, the RTC is engaged in internal processing, so read to and write from the S1 to W registers is inhibited. The 30-seconds ADJ bit is automatically cleared to 0 at the end of the 76.3 ∝ s.

3. CE register (control register E)(1) MASK bit (D0)

The MASK bit controls the STD.P pin output. The relationships between the MASK bit, ITRPT/STND bit, and STD.P pin output are as follows:

MASK	ITRPT/STND	STD.P pin output
0	0	Fixed-period pulse output mode
0	1	Fixed-period interrupt mode
1	0 or 1	Open

The timings of the MASK bit, ITRPT/STND bit, and STD.P pin output are as follows:

1.Fixed-period pulse output mode (ITRPT/STND=0)

MASK bit			0		1	0	1	0
IRQ FLAG bit
	0	1		0	1	0
*STD.P pin								Nothing is output because
								the MASK bit is at 1
								Output timing
								Automatic return

The output levels of the STD.P pin are low (down) and open circuit(up).

Page - 11 MQ - 162 - 03