LTC1325CSW datasheet(22/24 Pages) LINER

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LTC1325

wiper on a potentiometer between these two. Table 1

illustrates a complete 6-byte exchange. Note that the first

byte is padded with zeroes to align the A/D data and status

with byte boundaries.

SPCR = (SPIE = 0, SPE = 1, DWOM = 0, MSTR = 1,

CPOL = 0, CPHA = 0, SPR1 = 0, SPR0 = 1)

DDRD = (BIT7 = 0, BIT6 = 0, DDR5 = 1, DDR4 = 1,

DDR3 = 1, DDR2 = 0, DDR1 = 0, DDR0 = 1)

Table 1. 6-Byte Exchange SPI Communication with LTC1325

BYTE #1 TX

SCK

MOSI

PORTD.0

MISO

START MOD0

BYTE #1 RX

MOD1

BYTE #2 TX

SGL/

DIFF

MSBF

DS0

DS1

DS2

DIV0

DIV1

BYTE #2 RX

DIV2

BYTE #3 TX

DIV3

DR0

DR1

DR2

FSCLR

TO0

BYTE #3 RX

TO1

BYTE #4 TX

TO2

VR0

VR1

BYTE #4 RX

BYTE #5 TX

BYTE #5 RX

BYTE #6 TX

BATP

BYTE #6 RX

BATR

FMCV

FEVD

FHTF

FLTF

t0UT

LTC1325 • AI01

CLK

DIN

DOUT

68HC11

LTC1325

X = DON’T CARE

idle mode to minimize noise. The microprocessor

should either disregard readings or wait for a second

or so before taking a reading. This is to allow VCELL to

decay to the correct cell voltage. The worst case time

constant is 150k

Ω(CF).

10. Prior to the first START command, the battery divider

setting may be incorrect so that CF may charge to a

voltage that causes EDV, BATR or MCV faults. The

worst case time constant is as in (9). The micropro-

cessor should check faults during the transmission of

a START command and resend the START command

again when CF has been given enough time to charge

up to the correct value.

MICROPROCESSOR INTERFACES

The LTC1325 can interface directly to either synchronous,

serial or parallel I/O ports of most popular microproces-

sors. With a parallel port, 3 or 4 I/O lines can be pro-

grammed to form a serial link to the LTC1325.

Motorola SPI (68HC11)

The 68HC11 has a dedicated synchronous serial interface

called the Serial Peripheral Interface (SPI) which transfers

datawithMSB-firstandin8-bitincrements.Tocommunicate

with this microprocessor, the LTC1325 MSBF control bit

should be set to 1. The SPI has four lines: Master In Slave Out

(MISO), Master Out Slave In (MOSI), Serial Clock (SCK) and

Slave Select (SS). The 68HC11 is configured as a Master by

tying the SS line high. A control byte is written to the Serial

Peripheral Control Register (SPCR) to select master mode,

set baud rate and clock timing relationship. Another byte is

written to the Port D Direction Register (DDRD) to set MOSI,

SCK and bit 0 (CS of LTC1325) as outputs. The 68HC11

clocks in data from the LTC1325 simultaneously under the

control of SCK. The microprocessor transmits the LTC1325

commandwordin4bytes.Thisisfollowedby2moredummy

bytes (with all bits set low) in order to clock in the remaining

LTC1325 ADC and status bits.

This software example allows you to verify communica-

tions with the LTC1325. The command word configures

the LTC1325 to perform an A/D conversion on the general

purpose VIN input. VIN can be tied to GND or REG or to a

APPLICATIONS INFORMATION

LTC1325CSW Datasheet(PDF) 22 Page - Linear Technology

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