
AD9854 PRELIMINARY TECHNICAL DATA
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General Operation of the Serial Interface
7/16/99 REV.PRA
22
There are two phases to a communication cycle with the
AD9854/52. Phase 1 is the instruction cycle, which is the
writing of an instruction byte into the AD9854/52,
coincident with the first 8 SCLK rising edges. The
instruction byte provides the AD9854/52 serial port
controller with information regarding the data transfer
cycle, which is phase 2 of the communication cycle. The
Phase 1 instruction byte defines whether the upcoming data
transfer is read or write, and
the register address in which
to transfer data to/from.
The first eight SCLK rising edges of each communication
cycle are used to write the instruction byte into the
AD9854/52. The remaining SCLK edges are for phase 2 of
the communication cycle. Phase 2 is the actual data
transfer between the AD9854/52 and the system controller.
The number of data bytes transferred in Phase 2 of the
communication cycle is a function of the register address.
The AD9854/52 internal serial IO controller expects every
byte of the register being accessed to be transferred. Table
below describes how many bytes must be transferred
Serial Register
Address
0
1
2
3
4
5
6
7
8
9
A
B
Register Name
Phase OffsetTuning Word Register#1
Phase OffsetTuning Word Register #2
Frequency Tuning Word #1
Frequency Tuning Word #2
Delta FrequencyRegister
Update Clock Rate Register
Ramp Rate Clock Register
Control Register
I Path Digital Multiplier Register
Q Path Digital Multiplier Register
Shaped On-Off Keying Ramp Rate Register
Q DAC Register
Number of Bytes
Transferred
2 bytes
2 bytes
6 bytes
6 bytes
6 bytes
4 bytes
3 bytes
4 bytes
2 bytes
2 bytes
2 bytes
2 bytes
At the completion of any communication cycle, the
AD9854/52 serial port controller expects the next 8 rising
SCLK edges to be the instruction byte of the next
communication cycle. In addition, an active high input on
the IORESET pin immediately terminates the current
communication cycle. After IORESET returns low, the
AD9854/52 serial port controller requires the next 8 rising
SCLK edges to be the instruction byte of the next
communication cycle.
All data input to the AD9854/52 is registered on the rising
edge of SCLK. All data is driven out of the AD9854/52 on
the falling edge of SCLK.
Figures 2 and 3 are useful in understanding the general
operation of the AD9854/52 Serial Port.
Figure 2. Using SDIO as a Read/Write Transfer
SDIO
CS
INSTRUCTION
BYTE
DATA BYTE 1
DATA BYTE 2
DATA BYTE 3
DATA TRANSFER
INSTRUCTION
CYCLE