Datasheet

Data Sheet AD9910
Rev. D | Page 49 of 64
I/O_RESET—Input/Output Reset
I/O_RESET synchronizes the I/O port state machines without
affecting the contents of the addressable registers. An active
high input on the I/O_RESET pin causes the current communica-
tion cycle to abort. After I/O_RESET returns low (Logic 0),
another communication cycle can begin, starting with the
instruction byte write.
I/O_UPDATE—Input/Output Update
The I/O_UPDATE initiates the transfer of written data from
the I/O port buffer to active registers. I/O_UPDATE is active
on the rising edge, and its pulse width must be greater than one
SYNC_CLK period. It is either an input or output pin depending
on the programming of the internal I/O update active bit.
SERIAL I/O TIMING DIAGRAMS
Figure 55 through Figure 58 provide basic examples of the timing
relationships between the various control signals of the serial
I/O port. Most of the bits in the register map are not transferred
to their internal destinations until assertion of an I/O update,
which is not included in the timing diagrams that follow.
MSB/LSB TRANSFERS
The AD9910 serial port can support both most significant bit
(MSB) first or least significant bit (LSB) first data formats. This
functionality is controlled by Bit 0 in Control Function Register 1
(0x00). The default format is MSB first. If LSB first is active, all
data, including the instruction byte, must follow LSB-first conven-
tion. Note that the highest number found in the bit range column
for each register is the MSB, and the lowest number is the LSB
for that register (see the Register Map and Bit Descriptions
section and Table 17).
I
7
SDIO
INSTRUCTION CYCLE DATA TRANSFER CYCLE
SCLK
CS
I
6
I
5
I
4
I
3
I
2
I
1
I
0
D
7
D
6
D
5
D
4
D
3
D
2
D
1
D
0
06479-030
Figure 55. Serial Port Write Timing, Clock Stall Low
D
O7
INSTRUCTION CYCLE DATA TRANSFER CYCLE
DON'T CARE
I
7
I
6
I
5
I
4
I
3
I
2
I
1
I
0
SDIO
SCLK
CS
SDO
D
O6
D
O5
D
O4
D
O3
D
O2
D
O1
D
O0
06479-031
Figure 56. 3-Wire Serial Port Read Timing, Clock Stall Low
I
7
SDIO
INSTRUCTION CYCLE DATA TRANSFER CYCLE
SCLK
CS
I
6
I
5
I
4
I
3
I
2
I
1
I
0
D
7
D
6
D
5
D
4
D
3
D
2
D
1
D
0
06479-032
Figure 57. Serial Port Write Timing, Clock Stall High
I
7
SDIO
INSTRUCTION CYCLE DATA TRANSFER CYCLE
SCLK
CS
I
6
I
5
I
4
I
3
I
2
I
1
I
0
D
O7
D
O6
D
O5
D
O4
D
O3
D
O2
D
O1
D
O0
06479-033
Figure 58. 2-Wire Serial Port Read Timing, Clock Stall High