Analog Devices AD9609 Evaluation Board AD9609-65EBZ AD9609-65EBZ Scheda Tecnica

 

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The AD9609 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  
gives 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 documented in the Memory Map section. For 
detailed operational information, see the AN-877 Applica- 
tion Note, Interfacing to High Speed ADCs via SPI. 

Three pins define the SPI of this ADC: SCLK, SDIO, and CSB 
(see Table 14). The SCLK (a serial clock) is used to synchronize 
the read and write data presented from and to the ADC. SDIO 
(serial data input/output) is a dual-purpose pin that allows data to 
be sent 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 CSB, in conjunction with the rising edge of 
SCLK, determines the start of the framing. An example of the 
serial timing and its definitions can be found in Figure 54 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, as shown in Figure 54. 

All data is composed of 8-bit words. 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. This allows the serial 
data input/output (SDIO) pin to change direction from an input 
to an output at the appropriate point in the serial frame. 

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. 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. 

Data can be sent in MSB-first mode or in LSB-first mode. MSB 
first 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 AN-877 Application Note, Interfacing 
to High Speed ADCs via SPI. 

 

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