14

LTC1290

S

APPLICATI

I FOR ATIO

Microprocessor Interfaces

The LTC1290 can interface directly (without external hard-

ware) to most popular microprocessor (MPU) synchro-

nous serial formats (see Table 2). If an MPU without a

serial interface is used, then four of the MPU’s parallel port

lines can be programmed to form the serial link to the

LTC1290. Included here are two serial interface examples

and one example showing a parallel port programmed to

form the serial interface

Serial Port Microprocessors

Most synchronous serial formats contain a shift clock

(SCLK) and two data lines, one for transmitting and one for

receiving. In most cases data bits are transmitted on the

falling edge of the clock (SCLK) and captured on the rising

edge. However, serial port formats vary among MPU

manufactures as to the smallest number of bits that can be

sent in one group (e.g., 4-bit, 8-bit or 16-bit transfers).

They also vary as to the order in which the bits are

transmitted (LSB or MSB first). The following examples

show how the LTC1290 accommodates these differences.

Figure 4. CS Low During Conversion (CS Must go High to Low Once to Insure Proper Operation in this Mode)

B11 B10 B9

B8

B7

B6

B5

B4

B3

B2

B1

B0

B11 B10 B9

B8

B7

B6

B5

B4

B3

B2

B1

B0

SHIFT RESULT OUT

AND NEW ADDRESS IN

SCLK

CS

SAMPLE ANALOG

INPUT

SHIFT

MUX ADDRESS

IN

LTC1290 F04

48 TO 52

ACLK CYC

SCLK MUST

REMAIN LOW

DON’T CARE

Figure 3. CS High During Conversion

B11 B10 B9B8B7B6B5B4B3B2B1B0

B11 B10 B9

B8

B7

B6

B5

B4

B3

B2

B1

B0

SHIFT RESULT OUT

AND NEW ADDRESS IN

SCLK

CS

SAMPLE ANALOG

INPUT

SHIFT

MUX ADDRESS

IN

LTC1290 F03

48 TO 52

ACLK CYC

DON’T CARE