10

LTC1291

Table 1. Microprocessor with Hardware Serial Interfaces

Compatible with the LTC1291**

PART NUMBER

TYPE OF INTERFACE

Motorola

MC6805S2, S3

SPI

MC68HC11

SPI

MC68HC05

SPI

RCA

CDP68HC05

SPI

Hitachi

HD6305

SCI Synchronous

HD6301

SCI Synchronous

HD63701

SCI Synchronous

HD6303

SCI Synchronous

HD64180

SCI Synchronous

National Semiconductor

COP400 Family

COP800 Family

NS8050U

MICROWIRE/PLUS

HPC16000 Family

MICROWIRE/PLUS

Texas Instruments

TMS7002

Serial Port

TMS7042

Serial Port

TMS70C02

Serial Port

TMS70C42

Serial Port

TMS32011*

Serial Port

TMS32020*

Serial Port

TMS370C050

SPI

* Requires external hardware

** Contact factory for interface information for processors not on this list

Semiconductor Corp.

Unipolar Transfer Curve

0 0 0 0 0 0 0 0 0 0 0 1

0 0 0 0 0 0 0 0 0 0 0 0

1 1 1 1 1 1 1 1 1 1 1 1

1 1 1 1 1 1 1 1 1 1 1 0

•

•

•

1291 AI05b

Output Code

The LTC1291 performs a unipolar conversion. The follow-

ing shows the output code and transfer curve:

OUTPUT CODE

1 1 1 1 1 1 1 1 1 1 1 1

1 1 1 1 1 1 1 1 1 1 1 0

•

•

•

0 0 0 0 0 0 0 0 0 0 0 1

0 0 0 0 0 0 0 0 0 0 0 0

INPUT VOLTAGE

•

•

•

1LSB

0V

INPUT VOLTAGE

4.9988V

4.9976V

•

•

•

0.0012V

0V

1291 AI05a

Unipolar Output Code

Microprocessor Interfaces

The LTC1291 can interface directly (without external hard-

ware) to most popular microprocessors’s (MPU) synchro-

nous serial formats (see Table 1). If an MPU without a

dedicated serial port is used, then three of the MPU’s

parallel port lines can be programmed to form the serial

link to the LTC1291. Included here are one serial interface

example and one example showing a parallel port pro-

grammed to form the serial interface.

Motorola SPI (MC68HC11)

The MC68HC11 has been chosen as an example of an MPU

with a dedicated serial port. This MPU transfers data MSB

register starts the SPI process. With three 8-bit transfers,

the A/D result is read into the MPU. The second 8-bit

transfer clocks B11 through B8 of the A/D conversion

result into the processor. The third 8-bit transfer clocks the

remaining bits, B7 through B0, into the MPU. The data is

right justified in the two memory locations. ANDing the

bits. This operation was not included in the code. It can be

inserted in the data gathering loop or outside the loop

when the data is processed.

S

APPLICATI

I FOR ATIO