©2009 CADEKA Microcircuits LLC

www.cadeka.com

15

PRELIMINARY Data Sheet

Serial Interface

The CDK8307 configuration registers can be accessed through a serial interface formed by the pins SDATA (serial

interface data), SCLK (serial interface clock) and CSN (chip select, active low). The following occurs when CSN is set low:

n

Serial data are shifted into the chip

n

At every rising edge of SCLK, the value present at SDATA is latched

n

SDATA is loaded into the register every 24th rising edge of SCLK

Multiples of 24-bit words data can be loaded within a single active CSN pulse. If more than 24 bits are loaded into

SDATA during one active CSN pulse, only the first 24 bits are kept. The excess bits are ignored. Every 24-bit word is

divided into two parts:

n

The first eight bits form the register address

n

The remaining 16 bits form the register data

Acceptable SCLK frequencies are from 20MHz down to a few hertz. Duty-cycle does not have to be tightly controlled.

Timing Diagram

Figure 5 shows the timing of the serial port interface. Table 1 below explains the timing variables used in the Timing

Diagram.

CSN

A7

i

A6

A5

A4

A3

A2

A1

A0

D15 D14 D13 D12 D11 D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

SCLK

SDATA

Figure 5. Serial Port Interface Timing Diagram

Table 1. Serial Port Interface Timing Definitions

Parameter

Description

Minimum Value

Unit

Setup time between CSN and SCLK

8

ns

Hold time between CSN and SCLK

8

ns

SCLK high time

20

ns

SCLK low time

20

ns

SCLK period

50

ns

Data setup time

5

ns

Data hold time

5

ns

Register Initialization

Before CDK8307 can be used, the internal registers must be initialized to their default values. This can be done

immediately after applying supply voltage to the circuit. Initialization can be done in one of two ways:

1. By applying a low-going pulse on the RESET pin

2. By using the serial interface to set the RST bit high. Internal registers are reset to default values when this

bit is set. The RST bit is self-reset to zero. When using this method, do not apply any low-going pulse on the

RESETN pin.