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LTC1273

LTC1275/LTC1276

127356fa

APPLICATI

I FOR ATIO

OLD DATA

DB7-DB0

NEW DATA

DB7-DB0

TRACK

HOLD

DATA

BUSY

LTC1273/75/76 • F14

t 3

t CONV

t11

t10

t12

HBEN

NEW DATA

DB11-DB8

Figure 14. Slow Memory Mode, Two Byte Read Timing Diagram

Table 3. Slow Memory Mode, Two Byte Read Data Bus Status

Data Outputs

D3/11

D2/10

D1/9

D0/8

First Read

DB7

DB6

DB5

DB4

DB3

DB2

DB1

DB0

Second Read

Low

DB11

DB10

DB9

DB8

that the 4MSBs appear on data output D11...D8 during

both READ operations.

ROM Mode, Parallel Read (HBEN = LOW)

The ROM Mode avoids placing a microprocessor into a

WAIT state. A conversion is started with a READ opera-

tion, and the 12 bits of data from the previous conversion

are available on data outputs D11...D0/8 (see Figure 15

and Table 4). This data may be disregarded if not re-

quired. A second READ operation reads the new data

(DB11...DB0) and starts another conversion. A delay at

least as long as the ADC’s conversion time plus the 600ns

minimum delay between conversions must be allowed

between READ operations.

ROM Mode, Two Byte Read

As previously mentioned for a two byte read, only data

outputs D7...D0/8 are used. Conversion is started in the

normal way with a READ operation and the data output

status is the same as the ROM mode, Parallel Read (see

Figure 16 timing diagram and Table 5 data bus status).

Two more READ operations are required to access the new

conversion result. A delay equal at the ADCs’ conversion

time must be allowed between conversion start and the

third data READ operation. The second READ operation

with HBEN high disables conversion start and places the

high byte (4MSBs) on data outputs D3/11...D0/8. A third

read operation accesses the low data byte (DB7...DB0)

and starts another conversion. The 4MSBs appear on data

outputs D11...D8 during all three read operations.

MICROPROCESSOR INTERFACING

The LTC1273/LTC1275/LTC1276 allow easy interfac-

ing to digital signal processors as well as modern high

speed, 8-bit or 16-bit microprocessors. Here are sev-

eral examples.

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