Preliminary Technical Data
AD7415
C O NF IG U RAT IO N RE G IST E R (AD D RE SS 01H )
T he Configuration Register is an 8-bit read/write register
that is used to set the operating modes of the AD7415.
Only four of the MSBs are used (D7 to D4) to set the
operating modes, see T able 7. D0 to D5 are used for fac-
tory settings and must have zeros written to them during
normal operation.
sions, up to eight AD7415’s can be connected to a single,
serial bus, or the addresses can be set to avoid conflicts
with other devices on the bus.
T he serial bus protocol operates as follows:
1. T he master initiates data transfer by establishing a
ST ART condition, defined as a high to low transition
on the serial data line SDA whilst the serial clock line
SCL remains high. T his indicates that an address/data
stream will follow. All slave peripherals connected to
the serial bus respond to the ST ART condition, and
shift in the next 8 bits, consisting of a 7-bit address
(MSB first) plus a R/W bit, which determines the direc-
tion of the data transfer, i.e. whether data will be writ-
ten to or read from the slave device.
Table 6. Configur ation Register
D7
PD
0 *
D6
D5
D4
D3
D2 D1 D0
FLTR
1 *
T EST MODE
0’s*
*Default settings at Power-up.
T he peripheral whose address corresponds to the trans-
mitted address responds by pulling the data line low
during the low period before the ninth clock pulse,
known as the Acknowledge Bit. All other devices on the
bus now remain idle whilst the selected device waits for
data to be read from or written to it. If the R/W bit is a
0 then the master will write to the slave device. If the
R/W bit is a 1 the master will read from the slave de-
vice.
Table 7.
Configur ation Register Settings
D 7
D 6
Full Power-down if = 1
Bypass SDA & SCL filtering if = 0
2. Data is sent over the serial bus in sequences of 9 clock
pulses, 8 bits of data followed by an Acknowledge Bit
from the receiver of data. T ransitions on the data line
must occur during the low period of the clock signal
and remain stable during the high period, as a low to
high transition when the clock is high may be inter-
preted as a ST OP signal.
T E M P E RAT U RE VALU E RE G IST E R
T he T emperature Value Register is a 10-bit read-only
register which stores the temperature reading from the
ADC in twos complement format. T wo reads are neces-
sary to read data from this register. T he full theoretical
span of the ADC is 255oC, but in practice the temperature
measurement range is limited to the operating range of the
device, -55oC to +125oC for A-grade and -55oC to
+135oC for S-grade.
3. When all data bytes have been read or written, stop
conditions are established. In WRIT E mode, the master
will pull the data line high during the 10th clock pulse
to assert a ST OP condition. In READ mode, the mas-
ter device will pull the data line high during the low
period before the 9th clock pulse. T his is known as No
Acknowledge. T he master will then take the data line
low during the low period before the 10th clock pulse,
then high during the 10th clock pulse to assert a ST OP
condition.
Table 8.
D14
Tem per atur e Value Register (Fir st Read)
D15
D13
D12
D11
D10
D9
D8
M S B
B8
B7
B6
B5
B4
B3
B2
Table 9.
Tem per atur e Value Register (Second Read)
D7
D6
D5
D4
D3
D2
D1
D0
Any number of bytes of data may be transferred over the
serial bus in one operation, but it is not possible to mix
read and write in one operation, because the type of opera-
tion is determined at the beginning and cannot subse-
quently be changed without starting a new operation.
B1
L S B
N /A
N /A
N /A
N /A
N /A
N /A
AD 7415 SE RIAL INT E RF AC E
Control of the AD7415 is carried out via the I2C-compat-
ible serial bus. T he AD7415 is connected to this bus as a
slave device, under the control of a master device, e.g. the
processor.
WRITING TO TH E AD 7415
T here are two different writes for the AD7415. One is for
reading from either the Configuration Register or the
T emperature Value Register. T he other is for writing to
the Configuration Register only.
SE RIAL BUS AD D RE SS
Like all I2C-compatible devices, the AD7415 has a 7-bit
serial address. T he four MSBs of this address for the
AD7415 are set to 1001. T he AD7415 comes in four ver-
sions, the AD7415-0, AD7415-1, AD7415-2 and the
AD7415-3. T he first two versions have three different I2C
addresses available which are selected by either tying the
AS pin to GND, to VDD or letting the pin float (see
T able 1). By giving different addresses for the four ver-
Wr iting to the Addr ess P ointer Register for a subsequent
r ea d .
In order to read data from a particular register, the Ad-
dress Pointer Register must contain the address of that
register. If it does not, the correct address must be written
to the Address Pointer Register by performing a single-
REV. PrB
–7–
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