AD8120

Rev. 0 | Page 10 of 16

ANALOG CONTROL

A number of video transmission systems do not have a microcon-

troller embedded or otherwise available to provide digital control.

These systems require analog control. Potentiometer control is

one of the most common ways to implement analog control (see

Figure 25). To select analog control, set the MODE pin high.

on these inputs is 0 V to 2.0 V, although the actual control range

where delay changes take effect is smaller and lies within this larger

range. An internal ADC converts the analog control voltages

into binary delay codes; therefore, the analog control is discrete

with nominally 0.8 ns resolution. Figure 6 illustrates the typical

transfer characteristic between control voltage and delay code.

DIGITAL CONTROL

the SER_SEL pin high to select SPI mode, or set the SER_SEL

reading and writing the red, green, and blue registers.

Table 6. Read/Write Instruction and Color Registers

Operation

R/W Bit

C1 Bit

C0 Bit

Write Red

0

0

0

Read Red

1

0

0

Write Green

0

0

1

Read Green

1

0

1

Write Blue

0

1

0

Read Blue

1

1

0

SPI Control

The SPI bus operates in full-duplex mode and consists of four

digital lines: SDI, SDO, SCK, and CS.

Table 7. AD8120 SPI Pin Descriptions

Pin No.

Pin

Name

Description

29

SDI

Serial data input, master out slave in (MOSI)

2

SDO

Serial data output, master in slave out (MISO)

30

SCK

Serial clock from master

31

CS

Chip select; active low

The AD8120 is programmed in SPI mode using a 2-byte sequence

(see Table 8). Data is clocked into the SDI pin or clocked out of

the SDO pin on the rising edge of the clock, MSB first. The first

byte contains the read/write (R/W) instruction and the color reg-

ister address (see

). The second byte contains the delay

code to write to the part (R/

Table 6

W = 0) or the stored delay code to

read from the part (R/W = 1).

Figure 17 shows how to write Delay Code 42 to the green

register. Figure 18 shows how to read Delay Code 21 from

the blue register.

Table 8. SPI 2-Byte Sequence

Byte 1 (R/W Bit and Color Register)

Byte 2 (Data)

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

SDI

R/W

0

0

0

0

0

C1

C0

X

X

D5

D4

D3

D2

D1

D0

SDO

X

X

X

X

X

X

X

X

X

X

D5

D4

D3

D2

D1

D0