em3027 EM Microelectronic, em3027 Datasheet - Page 13

• Manufacturer Part Number: em3027
• Description: Real-time Clock With I2c Or Spi Interface, Crystal Temperature Compensation, Battery Switchover And Trickle Charger
• Manufacturer: EM Microelectronic

As the EM3027 has an integrated pull up resistor (100kΩ ) at SCL, the supply V
transmission, also if other IC's are addressed (due to EM3027 internal protection diode on SCL and SDA pins)
7.2
The SPI protocol is used to connect master and slaves.
4 wires are used: CS (Chip Select), SCK (serial clock), SI
(input data) and SO (output data). This chip can work as
slave only.
SPI is byte oriented protocol (MSB first order is used).
Data are changing on SCK falling edge and sampled on
the rising edge.
It’s possible to WRITE/READ the whole “page” during
one transmission with automatic address increment
feature. Only three less specified bits of the address are
incremented.
At the beginning of the transmission Chip Select goes to
active. First bit of data selects if READ or WRITE
Copyright © 2008, EM Microelectronic-Marin SA
07/08 – rev B
SCK
SO
CS
SI
How to perform READ/WRITE through SPI
R
Transmission START
R/W
A6
A5
A4
Figure 3 – SPI Write Transmission
Figure 2 – I2C communication
A3
A2
A1
A0
13
operation will follow after an address. The address is
composed of 7 bits.
If WRITE transmission is initiated then master continues
with data sending byte by byte. A less significant part of
the address is automatically incremented after each data
byte is received. The “page address” is fixed until a new
transmission is started. SO data output stays at ‘0’ during
the whole transmission.
If READ transmission is initiated then data are send after
the address by the slave. A less significant part of the
address is automatically incremented after each data
byte sent. The “page address” is not changing until a new
transmission is started. SI data input is not cared.
SO is in tri-state when CS inactive.
D7
D6
CC
...
...
...
must always be applied during an I2C
...
...
...
Transmission STOP
D3
D2
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EM3027
D1
D0