ADG2128 Data Sheet
Rev. D | Page 22 of 28
WRITE OPERATION
When writing to the ADG2128, 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 ADG2128 has been designed to work as a tool
for debug and can be used to output the status of any of the 96
switches of the device. The readback function is a 2-step
sequence that works as follows:
1. Select the relevant X line that you wish to 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
ADG2128 to tell the part that you would like to know the
status of those eight switches.
a. Enter the I
2
C address of the ADG2128, and set the
R/
W
bit to 0 to indicate that you are writing to the
device.
b. Enter the readback address for the X line of interest,
the addresses of which are shown in Table 8. Note that
the ADG2128 is expecting a 2-byte write; therefore, be
sure to enter another byte of don’t cares. (see Figure 35).
c. The ADG2128 then places the status of those eight
switches in a register that can be read back.
2. The second step involves reading back from the register
that holds the status of the eight switches associated with
your X line of choice.
a. As before, enter the I
2
C address of the ADG2128. This
time, set the R/
W
bit to 1 to indicate that you would
like to read back from the device.
b. As with a write to the device, the ADG2128 outputs 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, then the switch is closed (on); similarly,
if it is a 0, the switch is open (off).
The entire read sequence is shown in Figure 35.
05464-005
DATA AX3 AX2 AX1 AX0 AY2 AY1 AY0
A0 R/W
A1A2
x x x x x x x
SCL
SDA
DATA BYTEDATA BYTE
ACK
BY
SWITCH
STOP
COND
BY
MASTER
START
COND
BY
MASTER
ADDRESS BYTE
ACK
BY
SWITCH
ACK
BY
SWITCH
LDSW
Figure 34. Write Operation
Table 8. Readback Addresses for Each X Line
X Line RB7 RB6 RB5 RB4 RB3 RB2 RB1 RB0
X0 0 0 1 1 0 1 0 0
X1 0 0 1 1 1 1 0 0
X2 0 1 1 1 0 1 0 0
X3 0 1 1 1 1 1 0 0
X4 0 0 1 1 0 1 0 1
X5 0 0 1 1 1 1 0 1
X6 0 1 1 1 0 1 0 1
X7 0 1 1 1 1 1 0 1
X8 0 0 1 1 0 1 1 0
X9 0 0 1 1 1 1 1 0
X10 0 1 1 1 0 1 1 0
X11 0 1 1 1 1 1 1 0
