Epson RX-8581JE, RX-8581NB, RX-8581SA bit, bit, bit, bit, bit, bit, bit, bit, Read, A3 h, A2 h, [1010, Write, R/W bit, 1 (= Read), 0 (= Write), Transfer data, Slave address, 1)Data transfers

RX - 8581 SA / JE / NB

8.6.4.Data transfers and acknowledge responses during I2C-BUS communications1)Data transfers

Data transfers are performed in 8-bit (1 byte) units once the START condition has occurred. There is no limit on the amount (bytes) of data that are transferred between the START condition and STOP condition. (However, the transfer time must be no longer than 0.95 seconds.)

The address auto increment function operates during both write and read operations. After address Fh, incrementation goes to address 0h.

Updating of data on the transmitter (transmitting side)'s SDA line is performed while the SCL line is at low level. The receiver (receiving side) receives data while the SCL line is at high level.

SCL

SDA

Data is valid	Data can be
when data line is	changed
stable

∗Note with caution that if the SDA data is changed while the SCL line is at high level, it will be treated as a START, RESTART, or STOP condition.

2)Data acknowledge response (ACK signal)

When transferring data, the receiver generates a confirmation response (ACK signal, low active) each time an 8-bit data segment is received. If there is no ACK signal from the receiver, it indicates that normal communication has not been established. (This does not include instances where the master device intentionally does not generate an ACK signal.)

Immediately after the falling edge of the clock pulse corresponding to the 8th bit of data on the SCL line, the transmitter releases the SDA line and the receiver sets the SDA line to low (= acknowledge) level.

SCL from Master	1	2	8	9
SDA from transmitter (sending				Release SDA
side)
SDA from receiver (receiving				Low active
side)

ACK signal

After transmitting the ACK signal, if the Master remains the receiver for transfer of the next byte, the SDA is released at the falling edge of the clock corresponding to the 9th bit of data on the SCL line. Data transfer resumes when the Master becomes the transmitter.

When the Master is the receiver, if the Master does not send an ACK signal in response to the last byte sent from the slave, that indicates to the transmitter that data transfer has ended. At that point, the transmitter continues to release the SDA and awaits a STOP condition from the Master.

8.6.5. Slave address

The I2C bus device does not include a chip select pin such as is found in ordinary logic devices. Instead of using a chip select pin, slave addresses are allocated to each device.

All communications begin with transmitting the [START condition] + [slave address (+ R/W specification)]. The receiving device responds to this communication only when the specified slave address it has received matches its own slave address.

Slave addresses have a fixed length of 7 bits. This RTC's slave address is [1010 001∗ ]. An R/W bit ("*" above) is added to each 7-bit slave address during 8-bit transfers.

	Transfer data
Read	A3 h
Write	A2 h

		Slave address					R/W bit
bit 7	bit 6	bit 5	bit 4	bit 3	bit 2	bit 1	bit 0
1	0	1	0	0	0	1	1 (= Read)
							0 (= Write)

Page - 23 MQ372-02