DA6512.003
2 December, 2016
SERIAL DATA INTERFACE CONTROL
Serial Interface
MAS6512 can be operated either via 2-wire serial
I2C bus or via 4-wire serial SPI bus. Selection
between I2C and SPI communication is done by
XSPI pin. XSPI=high selects I2C and XSPI=low
selects SPI communication.
Digital interface includes also end of conversion
(EOC) and master reset (XCLR) pins. Rising edge
in the EOC pin indicates that the conversion is
ready and the result can be read out through serial
interface.
2-wire serial I2C bus type interface comprises of
serial clock input (SCL) and bi-directional serial data
(SDA) input/output. I2C bus is used to write
configuration data to sensor interface IC and read
the measurement result when A/D conversion has
been finished. The interface is also used for reading
the calibration EEPROM memory.
XCLR is used to reset the MAS6512. A reset
initializes registers (set to value 00HEX), counters
and the serial communication bus. Alternatively
device can be reset via serial bus by writing any
data to Reset register (address E0/60HEX). The
Reset register bits don’t have any function. Reading
from the reset register is not possible.
Note: The 2-wire I2C bus of MAS6512 supports only
basic I2C bus communication protocol but not for
example 10-bit addressing, arbitration and clock
stretching features of the I2C bus specification.
After connecting the supply voltage to MAS6512,
and before starting operating the device via the
serial bus, it is required to reset the device if the
supply voltage rise time has been longer than 1ms.
However it is recommended to reset the device
manually after every power up to guarantee proper
register settings after any VDD rise conditions
The alternative 4-wire serial SPI bus type interface
comprises of serial clock input (SCLK), serial data
input (MOSI), serial data output (MISO) and chip
select input (XCS).
I2C Bus Communication
In MAS6512 the I2C bus communication is selected
by setting XSPI pin high.
The programmable device address is located in the
EEPROM register C2HEX which has been factory
programmed to value ECHEX (%11101100) which is
the same as the fixed device address of MAS6512.
When unique device address is needed it can be
programmed to this register. The programmable
I2C device address is read from EEPROM memory
only during power on reset or manual reset
situations. To guarantee that the programmable
address is read from EEPROM the device can be
reset manually by using XCLR pin or Reset register
(E0/60HEX).
The I2C bus standard makes it possible to connect
several devices on same bus. The devices are
distinguished from each other by unique device
addresses. In MAS6512 there is both a hard wired
and programmable device address. Both hard wired
and programmable addresses can be used to
address MAS6512. The MAS6512 hard wired
device address is shown in the following table. The
LSB bit of the device address defines whether the
bus is configured to Read (1) or Write (0) operation.
Table 11. MAS6512 hard wired I2C bus device address (EC/EDHEX
)
A7
A6
A5
A4
A3
A2
A1
W/R
1
1
1
0
1
1
0
0/1
I2C Bus Protocol Definitions
Data transfer is initiated with a Start bit (S) when
SDA is pulled low while SCL stays high. Then, SDA
sets the transferred bit while SCL is low and the
data is sampled (received) when SCL rises. When
the transfer is complete, a Stop bit (P) is sent by
releasing the data line to allow it to be pulled up
while SCL is constantly high.
when SCL is high. Data at the SDA pin can change
value only when SCL is low.
Each SDA line byte transfer must contain 8-bits
where the most significant bit (MSB) always comes
first. Each byte has to be followed by an
acknowledge bit (see further below). The number of
bytes transmitted per transfer is unrestricted.
Figure 4 shows the start (S) and stop (P) bits and a
data bit. Data must be held stable at the SDA pin
18 (32)
MAS [ MICRO ANALOG SYSTEMS ]
