High-Precision Clock Generators

with Integrated VCXO

12

______________________________________________________________________________________

SMBCLK

AB

C

D

E

FG

H

I

J

K

SMBDATA

tSU:STA

tHD:STA

tLOW

tHIGH

tSU:DAT

tHD:DAT

tSU:STO tBUF

A = START CONDITION

B = MSB OF ADDRESS CLOCKED INTO SLAVE

C = LSB OF ADDRESS CLOCKED INTO SLAVE

D = R/W BIT CLOCKED INTO SLAVE

E = SLAVE PULLS SMBDATA LINE LOW

L

M

F = ACKNOWLEDGE BIT CLOCKED INTO MASTER

G = MSB OF DATA CLOCKED INTO MASTER

H = LSB OF DATA CLOCKED INTO MASTER

I = MASTER PULLS DATA LINE LOW

J = ACKNOWLEDGE CLOCKED INTO SLAVE

K = ACKNOWLEDGE CLOCK PULSE

L = STOP CONDITION

M = NEW START CONDITION

Figure 6. SMBus Read Timing Diagram

tCSS

tCSH

fSCL

tCSW

CS

SCLK

DIN

tDS

tDS

D0

D1

D14

D15

Figure 7. SPI Write Operation Timing Diagram

SLK

SDA

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

REGISTER ADDRESS

REGISTER DATA

CS

Figure 8. SPI Register Address and Data Configuration Function Setting Tables

SPI Interface

The SPI interface is activated when AD0 = AD1 = high.

The SPI port is a write-only interface, and it uses the

three inputs:

CS, SCL, and SDA. Bit D15 is always zero,

indicating the write-only mode, as shown in Figure 5.

D14–D8 are the register address bits and D7–D0 are

the data bits. In Table 4, the register address mapping

is still valid, except the first address bit on the left is not

used. D14 is the MSB of the address, and D7 is the

MSB of the data. D15–D0 are sent with MSB (D15) first.

The maximum SCL frequency is 2MHz.

To perform a write, set D15 = 0, drive

CS low, toggle

SCL to latch SDA data on the rising edge, then drive

CS high after 16 SCL cycles for two SCL cycles to sig-

nal the boundary of a 16-bit word (Figure 5). SCL must

be low when

CS falls at the start of a transmission.

Switching of SCL and SDA is ignored unless

CS is low.

Figure 7 shows the SPI write operation timing diagram

and Figure 8 shows SPI register address and data con-

figuration function setting tables.