AD9882 Analog Devices, AD9882 Datasheet - Page 31

• Manufacturer Part Number: AD9882
• Description: Dual Interface for Flat Panel Displays
• Manufacturer: Analog Devices

2-WIRE SERIAL CONTROL PORT
A 2-wire serial control interface is provided. Two AD9882
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 com-
prise 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
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 SA input pin in Table XLVIII), the AD9882
acknowledges by bringing SDA LOW on the ninth SCL pulse.
If the addresses do not match, the AD9882 does not acknowledge.
Bit 7
A6
(MSB)
1
1
REV. A
∑ Start signal
∑ Slave address byte
∑ Base register address byte
∑ Data byte to read or write
∑ Stop signal
SDA
SCL
Bit 6
A5
0
0
Table XLVIII. Serial Port Addresses
t
BUFF
Bit 5
A4
0
0
t
STAH
Bit 4
A3
1
1
t
DHO
Bit 3
A2
1
1
t
Figure 16. Serial Port Read/Write Timing
DAL
Bit 2
A1
0
0
t
DAH
t
DSU
Bit 1
A0
(LSB)
0
1
–31–
Data Transfer via Serial Interface
For each byte of data read or written, the MSB is the first bit of
the sequence.
If the AD9882 does not acknowledge the master device during a
write sequence, the SDA remains HIGH so the master can gener-
ate a stop signal. If the master device does not acknowledge the
AD9882 during a read sequence, the AD9882 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 AD9882 requires
that the 8-bit address of the control register of interest be written
after the slave address has been established. This control regis-
ter address is the base address for subsequent write operations.
The base address autoincrements by one for each byte of data
written after the data byte intended for the base address. If there
are more bytes transferred than there are available addresses, the
address will not increment and will remain at its maximum value
of 1Eh. Any base address higher than 1Eh will not produce an
acknowledge signal.
Data are read from the control registers of the AD9882 in a
similar manner. Reading requires two data transfer operations:
The base address must be written with the R/W bit of the slave
address byte LOW to set up a sequential read operation.
Reading (the R/W bit of the slave address byte HIGH) begins at
the previously established base address. The address of the read
register autoincrements after each byte is transferred.
To terminate a read/write sequence to the AD9882, a stop signal
must be sent. A stop signal comprises a LOW-to-HIGH transition
of SDA while SCL is HIGH. The timing for the read/write is
shown in Figure 16, and a typical byte transfer is shown in
Figure 17.
A repeated start signal occurs when the master device driving the
serial interface generates a start signal without first generating a
stop signal to terminate the current communication. This is used
to change the mode of communication (read, write) between the
slave and master without releasing the serial interface lines.
t
STASU
t
STOSU
AD9882