AD9985/PCB AD [Analog Devices], AD9985/PCB Datasheet - Page 26

• Manufacturer Part Number: AD9985/PCB
• Description: 110 MSPS/140 MSPS Analog Interface for Flat Panel Displays
• Manufacturer: AD [Analog Devices]

AD9985
2-WIRE SERIAL CONTROL PORT
A 2-wire serial control interface (I
AD9985 devices may be connected to the 2-wire serial interface,
with each device having a unique address.
The 2-wire serial interface comprises a clock (SCL) and a
bidirectional data (SDA) pin. The analog flat panel interface
acts as a slave for receiving and transmitting data over the serial
interface. When the serial interface is not active, the logic levels
on SCL and SDA are pulled high by external pull-up resistors.
Data received or transmitted on the SDA line must be stable for
the duration of the positive-going SCL pulse. Data on SDA must
change only when SCL is low. If SDA changes state while SCL is
high, the serial interface interprets that action as a start or stop
sequence.
There are five components to serial bus operation:
•
•
•
•
•
When the serial interface is inactive (SCL and SDA are high),
communications are initiated by sending a start signal. The start
signal is a high-to-low transition on SDA while SCL is high.
This signal alerts all slaved devices that a data transfer sequence
is coming.
The first eight bits of data transferred after a start signal
comprise a 7-bit slave address (the first seven bits) and a single
R/ W bit (the eighth bit). The R/ W bit indicates the direction of
Start Signal
Slave Address Byte
Base Register Address Byte
Data Byte to Read or Write
Stop Signal
SDA
SCL
t
t
STAH
BUFF
2
C) is provided. Up to two
t
DHO
t
DAL
Figure 12. Serial Port Read/Write Timing
t
DAH
t
DSU
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data transfer, read from (1) or write to (0) the slave device. If the
transmitted slave address matches the address of the device (set
by the state of the SA1-0 input pins in Table 42), the AD9985
acknowledges by bringing SDA low on the ninth SCL pulse. If
the addresses do not match, the AD9985 does not acknowledge.
Table 42. Serial Port Addresses
Bit 7
A
(MSB)
1
1
DATA TRANSFER VIA SERIAL INTERFACE
For each byte of data read or written, the MSB is the first bit of
the sequence.
If the AD9985 does not acknowledge the master device during a
write sequence, the SDA remains high so the master can
generate a stop signal. If the master device does not acknowl-
edge the AD9985 during a read sequence, the AD9985
interprets this as “end of data. ” The SDA remains high so the
master can generate a stop signal.
Writing data to specific control registers of the AD9985 requires
that the 8-bit address of the control register of interest be
written after the slave address has been established. This control
register address is the base address for subsequent write opera-
tions. The base address autoincrements by one for each byte of
data written after the data byte intended for the base address.
6
t
STASU
Bit 6
A
0
0
5
Bit 5
A
0
0
4
Bit 4
A
1
1
t
3
STOSU
Bit 3
A
1
1
2
Bit 2
A
0
0
1
Bit 1
A
0
1
0