LTC2408C datasheet(30/36 Pages) LINER

30 / 36 page

LTC2404/LTC2408

APPLICATIONS INFORMATION

DIN1

EQU

$00

This memory location holds the LTC2408’s bits 31 - 24

DIN2

EQU

$01

This memory location holds the LTC2408’s bits 23 - 16

DIN3

EQU

$02

This memory location holds the LTC2408’s bits 15 - 08

DIN4

EQU

$03

This memory location holds the LTC2408’s bits 07 - 00

MUX

EQU

$04

This memory location holds the MUX address data

***************************************

* Start GETDATA Routine

***************************************

ORG

$C000

Program start location

LDS

$CFFF

Top of C page RAM, beginning location of stack

INIT1

LDAA

#$2F

-,-,1,0;1,1,1,1

-, -, SS*-Hi, SCK-Lo, MOSI-Hi, MISO-Hi, X, X

STAA

PORTD

Keeps SS* a logic high when DDRD, bit 5 is set

LDAA

#$38

-,-,1,1;1,0,0,0

STAA

DDRD

SS* , SCK, MOSI are configured as Outputs

MISO, TxD, RxD are configured as Inputs

* DDRD’s bit 5 is a 1 so that port D’s SS* pin is a general output

LDAA

#$50

STAA

SPCR

The SPI is configured as Master, CPHA = 0, CPOL = 0

and the clock rate is E/2

(This assumes an E-Clock frequency of 4MHz. For higher

E-Clock frequencies, change the above value of $50 to a

value that ensures the SCK frequency is 2MHz or less.)

GETDATA PSHX

PSHY

PSHA

LDX

#$0

The X register is used as a pointer to the memory

locations that hold the conversion data

LDY

#$1000

*******************************

* The next routine sends data to the *

* LTC2408 an sets its MUX channel

*******************************

LDAA

$MUX

Retrieve MUX address

ORAA

#$08

Set the MUX’s ENABLE bit

STAA

SPDR

Transfer Accum. A contents to SPI register to initiate

serial transfer

WAITMUX LDAA

SPSR

Get SPI transfer status

BPL

WAITMUX If the transfer is not finished, read status

***************************************

* Enable the LTC2408

***************************************

BCLR

PORTD,Y %00100000 This sets the SS* output bit to a logic

low, selecting the LTC2408

***************************************

* The next short loop waits for the

* LTC2408’s conversion to finish before

* starting the SPI data transfer

***************************************

CONVEND LDAA

PORTD

Retrieve the contents of port D

ANDA

#%00000100

Look at bit 2

Bit 2 = Hi; the LTC2408’s conversion is not

complete

Bit 2 = Lo; the LTC2408’s conversion is complete

BNE

CONVEND

Branch to the loop’s beginning while bit 2 remains

high

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