Datasheet

AD9508 Data Sheet
Rev. B | Page 12 of 40
Pin No. Mnemonic Description
18
ARESET
E
CMOS Input. Device Reset. When this active low pin is asserted, the internal register settings enter their
default state after the
ARESET
E
A
is released. Note that ARESET
E
A
also serves as a power-down of the device
while an active low signal is applied to the pin. The
ARESET
E
A
pin has an internal 24 kΩ pull-up resistor.
19 SCLK/SCL/S0
Serial Programming Clock/Data Clock/Programming Pin. Multipurpose pin controlled by the PROG_SEL
pin used for serial programming clock (SCLK) in SPI mode or data clock (SCL) for serial programming in
I
2
C Mode. The PROG_SEL pin determines which programming mode is used. In pin programming
mode, this pin becomes S0. In this mode, S0 is hardwired with a resistor to either VDD or ground. The
resistor value and resistor biasing determine the channel divider values for the outputs on Pin 2 and
Pin 3. See the Pin Strapping to Program on Power-Up section for more details.
20
ASYNC
E
Clock Synchronization. When this pin is active low, the output drivers are held static and then
synchronized on a low-to-high transition of this pin. The
ASYNC
E
A
pin has an internal 24 kΩ pull-up
resistor.
21 CLK
Differential Clock Input or Single-Ended CMOS Input. Whether this pin serves as the differential clock
input or the single-ended CMOS input depends on the logic state of the IN_SEL pin.
22
ACLK
E
Complementary Differential Clock Input.
23
IN_SEL
CMOS Input. A logic high configures the CLK and ACLK
E
A
inputs for a differential input signal. A logic low
configures the input for single-ended CMOS applied to the CLK pin. AC-couple the unused
ACLK
E
A
to
ground with a 0.1 μF capacitor.
24 SDIO/SDA/S1
Serial Data Input and Output (SPI)/Serial Data (I
2
C)/Pin Programming. Pin 24 is a multipurpose input
controlled by the PROG_SEL pin used for SPI (SDIO), I
2
C (SDA), and pin strapping modes (S1). When the
device is in 4-wire SPI mode, data is written via SDIO. In 3-wire mode, both data reads and writes occur
on this pin. There is no internal pull-up/pull-down resistor on this pin. In I
2
C mode, SDA serves as the
serial data pin. The PROG_SEL pin determines which programming mode is used. In pin programming
mode, this pin becomes S1. In this mode, S1 is hardwired with a resistor to either VDD or ground. The
resistor value and resistor biasing determine the channel divider values for the outputs on Pin 7 and
Pin 8. See the Pin Strapping to Program on Power-Up section for more details.
EP Exposed Pad. The exposed die pad must be connected to ground (VSS).