Analog Devices AD9253 Evaluation Board AD9253-125EBZ AD9253-125EBZ Fiche De Données

 

Rev. 0 | Page 31 of 40 

The 

 serial port interface (SPI) allows the user to configure 

the converter for specific functions or operations through a 
structured register space provided inside the ADC. The SPI  
offers the user added flexibility and customization, depending on 
the application. Addresses are accessed via the serial port and 
can be written to or read from via the port. Memory is organized 
into bytes that can be further divided into fields, which are docu-
mented in the Memory Map section. For detailed operational 
information, see the 

, Interfacing to 

High Speed ADCs via SPI. 

Three pins define the SPI of this ADC: the SCLK pin, the SDIO 
pin, and the CSB pin (see Table 15). The SCLK (a serial clock) is 
used to synchronize the read and write data presented from and 
to the ADC. The SDIO (serial data input/output) is a dual-
purpose pin that allows data to be sent to and read from the 
internal ADC memory map registers. The CSB (chip select bar) 
is an active low control that enables or disables the read and 
write cycles. 

SCLK 

Serial clock. The serial shift clock input, which is used to 
synchronize serial interface reads and writes.  

SDIO 

Serial data input/output. A dual-purpose pin that 
typically serves as an input or an output, depending on 
the instruction being sent and the relative position in the 
timing frame.  

CSB 

Chip select bar. An active low control that gates the read 
and write cycles.  

 

The falling edge of the CSB, in conjunction with the rising edge 
of the SCLK, determines the start of the framing. An example of 
the serial timing and its definitions can be found in Figure 74 
and Table 5.  

Other modes involving the CSB are available. The CSB can be 
held low indefinitely, which permanently enables the device; 
this is called streaming. The CSB can stall high between bytes to 
allow for additional external timing. When CSB is tied high, SPI 
functions are placed in high impedance mode. This mode turns 
on any SPI pin secondary functions.  

During an instruction phase, a 16-bit instruction is transmitted. 
Data follows the instruction phase, and its length is determined 
by the W0 and W1 bits.  

In addition to word length, the instruction phase determines 
whether the serial frame is a read or write operation, allowing 
the serial port to be used both to program the chip and to read 
the contents of the on-chip memory. The first bit of the first byte in 
a multibyte serial data transfer frame indicates whether a read 
command or a write command is issued. If the instruction is a 
readback operation, performing a readback causes the serial 
data input/output (SDIO) pin to change direction from an input to 
an output at the appropriate point in the serial frame. 

All data is composed of 8-bit words. Data can be sent in MSB-
first mode or in LSB-first mode. MSB-first mode is the default 
on power-up and can be changed via the SPI port configuration 
register. For more information about this and other features, 
see the 

, Interfacing to High Speed 

ADCs via SPI. 

 

10

06

5-

0

78