ADT7518 
 
Rev. A | Page 34 of 40 
A
B
CS
(START HIGH)
SPI LOCKED ON
THIRD RISING EDGE
C
SPI FRAMING
EDGE
A
B
CS
(START LOW)
SPI LOCKED ON
THIRD RISING EDGE
C
SPI FRAMING
EDGE
 
Figure 53. Serial InterfaceSelecting and Locking SPI Protocol 
 
To select and lock the interface into the SPI mode, a number of 
pulses must be sent down the CS
 line (Pin 4). The following 
section describes how this is done. 
Once the SPI communication protocol has been locked in, it 
cannot be unlocked while the device is still powered up. Bit D0 
of the SPI lock status register (Address 7Fh) is set to 1 when a 
successful SPI interface lock has been accomplished. To reset 
the serial interface, the user must power down the part and 
power it up again. A software reset does not reset the serial 
interface. 
Serial Interface Selection 
The 
CS
 line controls the selection between I
2
C and SPI.  
Figure 53 shows the selection process necessary to lock the SPI 
interface mode. 
To communicate to the ADT7518 using the SPI protocol, send 
three pulses down the 
CS
 line as shown in Figure 53. On the 
third rising edge (marked as C in Figure 53), the part selects and 
locks the SPI interface. The user is now limited to communi-
cating to the device using the SPI protocol. 
As per most SPI standards, the CS line must be low during 
every SPI communication to the  ADT7518 and high all other 
times. Typical examples of how to connect the dual interface as 
I
2
C or SPI is shown in Figure 54 and Figure 55. The following 
sections describe in detail how to use the I
2
C and SPI protocols 
associated with the ADT7518. 
ADT7518
CS
SDA
SCL
ADD
V
DD
V
DD
I
2
C ADDRESS = 1001 000
10k&
10k&
 
Figure 54. Typical I
2
C Interface Connection 
ADT7518
SCLK
DOUT
CS
V
DD
LOCK AND
SELECT SPI
SPI FRAMING
EDGE
820&
820&
820&
DIN
 
Figure 55. Typical SPI Interface Connection 
I
2
C Serial Interface 
Like all I
2
C-compatible devices, the ADT7518 has a 7-bit serial 
address. The four MSBs of this address for the ADT7518 are set 
to 1001. The three LSBs are set by Pin 11, ADD. The ADD pin 
can be configured three ways to give three different address 
options: low, floating, and high. Setting the ADD pin low gives a 
serial bus address of 1001 000, leaving it floating gives the 
address 1001 010, and setting it high gives the address 1001 011. 
The recommended pull-up resistor value is 10 k&. 
There is an enable/disable bit for the SMBus timeout. When this 
is enabled, the SMBus will time out after 25 ms of no activity. To 
enable it, set Bit 6 of the Control Configuration 2 register. The 
power-on default is with the SMBus timeout disabled.  
The ADT7518 supports SMBus packet error checking (PEC), 
but its use is optional. It is triggered by supplying the extra 
clocks for the PEC byte. The PEC is calculated using CRC-8. 
The frame clock sequence (FCS) conforms to CRC-8 by the 
polynominal 
( )
1
1
2
8
+
+
+
=
x
x
x
x
C
 
Consult the SMBus specification (www.smbus.org) for more 
information.