RS5C314

3

The real-time clock becomes accessible by switching the CE pin from the low level to high level to enable

interfacing with the CPU and then inputting setting data (control bits and address bits) to the SIO pin in synchronization with

shift clock pulses from the SCLK pin.

The input data are registered in synchronization with the rising edge of the SCLK. When the data is read, the read cycle shall

be set by control bits.

2.1 Read Cycle Flow

1. The CE pin is switched from the low level to the high level.

2. Four control bits (with the first bit ignored) and four read address bits are input from the SIO pin. At this time,

control bits R/W and AD are set equally to 1 while a control bit DT is set to 0.

3. The SIO pin enters the output mode at the falling edge of the shift clock pulse 2B from the SCLK pinwhile the

four read bits (MSB

→LSB) at designated addresses are output at the falling edge of the shift clock pulse 5B (see

the figure below).

4. Then, the SIO pin returns to the input mode at the falling edge of the shift clock pulse 1C. Afterwards control bits

and address bits are input at the shift clock pulses 1C in the same manner as at the shift clock pulse 1A.

5. At the end of read cycle, the CE pin is switched from the high level to the low level (after

of the eighth shift clock pulse from the SCLK pin). (Following on read cycle, write operation can be performed by

setting control bits in the write mode at the shift clock pulse 1C and later with the CE pin held at the high level.)

R/W: Establishes the read mode when set to 1, and the write mode when set to 0.

AD: Writes succeeding address bits (A3 to A0) to the address register when set to 1 with the DT

bit set to 0 and performs no such write operation in any other case.

DT: Writes data bits (D3 to D0) to the counter or the register specified by the address register

which has written just before when set to 1 with the R/W and AD bits set equally to 0 and

performs no such write operation in any other case.

A3 to A0: Inputs the bits MSB to LSB in the address table describing the functions.

• Control bits

• Address bits

2. Read Data

1A

2A

3A

4A

5A

6A

7A

8A

1B

2B

3B

4B

5B

6B

7B

8B

1C

2C

3C

R/W

AD

DT

A3

A2

A1

A0

—

—

—

D3

D2

D1

D0

R/W

AD

*

CE

SCLK

Input to

SIO pin

Output from

SIO pin

(Internal processing)

Reading to shift register

Writing to

address resister

Setting of

control bit

Control bits

Address bits

(Hi-z)

(Hi-z)

(Hi-z)

Read data

Setting of

SIO pin in

output mode

Shifting data

Setting of SIO pin in

input mode

*

the

mark indicates data which are available when the SIO pin is held at the high, low, or Hiz level ;

and the diagonaliy shaded area indicates high or low.

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