AD9136-EBZ datasheet(23/117 Pages) AD

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Data Sheet

AD9135/AD9136

Rev. C | Page 23 of 117

SERIAL PORT OPERATION

The serial port is a flexible, synchronous serial communications

port that allows easy interfacing with many industry-standard

microcontrollers and microprocessors. The serial input/output

(I/O) is compatible with most synchronous transfer formats,

including both the Motorola SPI and Intel® SSR protocols. The

interface allows read/write access to all registers that configure

the AD9135/AD9136. MSB first or LSB first transfer formats are

supported. The serial port interface can be configured as a 4-wire

interface or a 3-wire interface in which the input and output share

a single-pin I/O (SDIO).

Figure 38. Serial Port Interface Pins

There are two phases to a communication cycle with the

AD9135/AD9136. Phase 1 is the instruction cycle (the writing

of an instruction byte into the device), coincident with the first

16 SCLK rising edges. The instruction word provides the serial

port controller with information regarding the data transfer cycle,

Phase 2 of the communication cycle. The Phase 1 instruction

word defines whether the upcoming data transfer is a read or

write, along with the starting register address for the following

data transfer.

A logic high on the CS pin followed by a logic low resets the

serial port timing to the initial state of the instruction cycle.

From this state, the next 16 rising SCLK edges represent the

instruction bits of the current I/O operation.

The remaining SCLK edges are for Phase 2 of the communication

cycle. Phase 2 is the actual data transfer between the device and

the system controller. Phase 2 of the communication cycle is a

transfer of one or more data bytes. Eight × N SCLK cycles are

needed to transfer N bytes during the transfer cycle. Registers

change immediately upon writing to the last bit of each transfer

byte.

DATA FORMAT

The instruction byte contains the information shown in Table 13.

Table 13. Serial Port Instruction Word

I[15] (MSB)

I[14:0]

R/W

A[14:0]

R/W, Bit 15 of the instruction word, determines whether a read

or a write data transfer occurs after the instruction word write.

Logic 1 indicates a read operation, and Logic 0 indicates a write

operation.

A14 to A0, Bit 14 to Bit 0 of the instruction word, determine the

communication cycle. For multibyte transfers, A[14:0] is the

starting address. The remaining register addresses are generated

by the device based on the address increment bits. If the address

increment bits are set high (Register 0x000, Bit 5 and Bit 2),

multibyte SPI writes start at A[14:0] and increment by 1 every

8 bits sent/received. If the address increment bits are set to 0,

the address decrements by 1 every 8 bits.

SERIAL PORT PIN DESCRIPTIONS

Serial Clock (SCLK)

The serial clock pin synchronizes data to and from the device

and runs the internal state machines. The maximum frequency

of SCLK is 10 MHz. All data input is registered on the rising edge

of SCLK. All data is driven out on the falling edge of SCLK.

Chip Select (CS)

An active low input starts and gates a communication cycle. CS

allows more than one device to be used on the same serial

communications lines. The SDIO pin goes to a high impedance

state when this input is high. During the communication cycle,

chip select must stay low.

Serial Data I/O (SDIO)

This pin is a bidirectional data line. In 4-wire mode, this pin

acts as the data input, and SDO acts as the data output.

SERIAL PORT OPTIONS

The serial port can support both MSB first and LSB first data

formats. This functionality is controlled by the LSB first bits

(Register 0x000, Bit 6 and Bit 1). The default is MSB first

(LSBFIRST/LSBFIRST_M = 0).

When the LSB first bits = 0 (MSB first), the instruction and data

bits must be written from MSB to LSB. R/W is followed by

A[14:0] as the instruction word, and D[7:0] is the data-word.

When the LSB first bits = 1 (LSB first), the opposite is true.

A[0:14] is followed by R/W, which is subsequently followed by

D[0:7].

The serial port supports a 3-wire or 4-wire interface. When the

SDO active bits = 1 (Register 0x000, Bit 4 and Bit 3), a 4-wire

interface with a separate input pin (SDIO) and output pin (SDO)

is used. When the SDO active bits = 0, the SDO pin is unused

and the SDIO pin is used for both input and output.

SCLK

SDIO

SDO

SPI

PORT

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