LTC1291 Linear Technology, LTC1291 Datasheet - Page 10

• Manufacturer Part Number: LTC1291
• Description: Single Chip 12-Bit Data Acquisition System
• Manufacturer: Linear Technology

LTC1291
A
Output Code
The LTC1291 performs a unipolar conversion. The follow-
ing shows the output code and transfer curve:
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
-first and in 8-bit increments. The D
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
second byte with 0D
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.
10
PPLICATI
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
OUTPUT CODE
•
•
•
Unipolar Output Code
O
U
HEX
S
INPUT VOLTAGE
V
V
REF
REF
clears the four most significant
I FOR ATIO
1LSB
U
0V
– 1LSB
– 2LSB
•
•
•
IN
INPUT VOLTAGE
W
(V
word sent to the data
4.9988V
4.9976V
0.0012V
REF
0V
•
•
•
= 5V)
1291 AI05a
U
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
•
•
•
Table 1. Microprocessor with Hardware Serial Interfaces
Compatible with the LTC1291**
PART NUMBER
Motorola
MC6805S2, S3
MC68HC11
MC68HC05
RCA
CDP68HC05
Hitachi
HD6305
HD6301
HD63701
HD6303
HD64180
National Semiconductor
COP400 Family
COP800 Family
NS8050U
HPC16000 Family
Texas Instruments
TMS7002
TMS7042
TMS70C02
TMS70C42
TMS32011*
TMS32020*
TMS370C050
* Requires external hardware
** Contact factory for interface information for processors not on this list
†
MICROWIRE and MICROWIRE/PLUS are trademarks of National
Semiconductor Corp.
Unipolar Transfer Curve
TYPE OF INTERFACE
SPI
SPI
SPI
SPI
SCI Synchronous
SCI Synchronous
SCI Synchronous
SCI Synchronous
SCI Synchronous
MICROWIRE
MCROWIRE/PLUS
MICROWIRE/PLUS
MICROWIRE/PLUS
Serial Port
Serial Port
Serial Port
Serial Port
Serial Port
Serial Port
SPI
†
†
1291 AI05b
V
IN