adg2108 Analog Devices, Inc., adg2108 Datasheet - Page 22

• Manufacturer Part Number: adg2108
• Description: I 2 C Cmos 8 ? 10 Unbuffered Analog Switch Array With Dual/single Supplies
• Manufacturer: Analog Devices, Inc.

ADG2108
WRITE OPERATION
When writing to the ADG2108, the user must begin with an
address byte and R/ W bit, after which the switch acknowledges
that it is prepared to receive data by pulling SDA low. This
address byte is followed by the two 8-bit words. The write
operations for the switch array are shown in Figure 34. Note
that it is only the condition of the switch corresponding to the
bits in the data bytes that changes state. All other switches retain
their previous condition.
READ OPERATION
Readback on the ADG2108 is designed to work as a tool for
debug and can be used to output the status of any of the
80 switches of the device. The readback function is a two-step
sequence that works as follows:
1.
SDA
Table 8. Readback Addresses for Each X Line
X Line
X0
X1
X2
X3
X4
X5
X6
X7
X8
X9
SCL
MASTER
a.
START
Select the relevant X line to be read back from. Note that
there are eight switches connecting that X line to the eight Y
lines. The next step involves writing to the ADG2108 to tell
the part to reveal the status of those eight switches.
COND
BY
Enter the I
R/ W to 0 to indicate a write to the device.
ADDRESS BYTE
RB7
0
0
0
0
0
0
0
0
0
0
2
C address of the ADG2108, and set the
A2
A1
RB6
1
1
0
0
1
1
0
0
1
1
A0
R/W
SWITCH
ACK
BY
DATA
RB5
1
1
1
1
1
1
1
1
1
1
AX3
AX2
Figure 34. Write Operation
Rev. 0 | Page 22 of 28
AX1
DATA BYTE
RB4
1
1
1
1
1
1
1
1
1
1
AX0
AY2
2.
The entire read sequence is shown in Figure 35.
AY1
b.
c.
The second step involves reading back from the register
that holds the status of the eight switches associated with
the X line of choice.
a.
b.
AY0
RB3
0
1
0
1
0
1
0
1
0
0
SWITCH
Enter the readback address for the X line of interest,
the addresses of which are shown in Table 8. Note that
the ADG2108 is expecting a 2-byte write; therefore, be
sure to enter another byte of don’t cares (see Figure 35).
The ADG2108 then places the status of those eight
switches in a register than can be read back.
As before, enter the I
As with a write to the device, the ADG2108 outputs
time, set the R/ W to 1 to indicate a readback from the
device.
a 2-byte sequence during readback. Therefore, the
first eight bits of data out that are read back are all 0s.
The next eight bits of data that come back are the status
of the eight Y lines attached to that particular X line.
If the bit is a 1, the switch is closed (on); similarly, if the
bit is a 0, the switch is open (off).
ACK
BY
x
x
RB2
1
1
1
1
1
1
1
1
1
1
x
x
DATA BYTE
2
C address of the ADG2108. This
x
RB1
0
0
0
0
0
0
1
1
1
1
x
x
LDSW
SWITCH
ACK
BY
RB0
0
0
1
1
1
1
0
0
0
0
MASTER
STOP
COND
BY