Datasheet

LTC1096/LTC1096L
LTC1098/LTC1098L
25
10968fc
MICROPROCESSOR INTERFACES
The LTC1096(L)/LTC1098(L) can interface directly (without
external hardware to most popular microprocessor (MPU)
synchronous serial formats (see Table 1). If an MPU without
a dedicated serial port is used, then three or four of the
MPU’s parallel port lines can be programmed to form the
serial link to the LTC1096(L)/LTC1098(L). Included here
is one serial interface example and one example showing
a parallel port programmed to form the serial interface.
Motorola SPI (MC68HC05C4,CM68HC11)
The MC68HC05C4 has been chosen as an example of
an MPU with a dedicated serial port. This MPU transfer
data MSB-fi rst and in 8-bit increments. With two 8-bit
transfers, the A/D result is read into the MPU. The fi rst
8-bit transfer sends the D
IN
word to the LTC1098(L) and
clocks into the processor. The second 8-bit transfer clocks
the A/D conversion result, B7 through B0, into the MPU.
ANDing the fi rst MUP received byte with 00Hex clears the
fi rst byte. Notice how the position of the start bit in the
fi rst MPU transmit word is used to position the A/D result
right-justifi ed in two memory locations.
APPLICATIONS INFORMATION
TYPICAL APPLICATIONS
Effective Number of Bits
The effective number of bits (ENOBs) is a measurement
of the resolution of an A/D and is directly related to the
S/(N + D) by the equation:
ENOB = [S/(N + D) –1.76]/6.02
where S/(N + D) is expressed in dB. At the maximum sam-
pling rate of 33kHz the LTC1096 maintains 7.5 ENOBs or
better to 40kHz. Above 40kHz the ENOBs gradually decline,
as shown in Figure 12, due to increasing second harmonic
distortion. The noise fl oor remains approximately 70dB.
Figure 12. Dynamic Accuracy Is Maintained Up to an Input
Frequency of 40kHz
INPUT FREQUENCY (kHz)
0
EFFECTIVE NUMBER OF BITS (ENOBs)
3
4
5
10968 F12
2
1
0
20 40
6
7
8
f
SAMPLE
= 31.25kHz
Table 1. Microprocessor with Hardware Serial Interfaces
Compatible with the LTC1096(L)/LTC1098(L)
PART NUMBER TYPE OF INTERFACE
Motorola
MC6805S2,S3
MC68HC11
MC68HC05
SPI
SPI
SPI
RCA
CDP68HC05 SPI
Hitachi
HD6305
HD63705
HD6301
HD63701
HD6303
HD64180
SCI Synchronous
SCI Synchronous
SCI Synchronous
SCI Synchronous
SCI Synchronous
CSI/O
National Semiconductor
COP400 Family
COP800 Family
NS8050U
HPC16000 Family
MICROWIRE™
MICROWIRE/PLUS™
MICROWIRE/PLUS
MICROWIRE/PLUS
Texas Instruments
TMS7002
TMS7042
TMS70C02
TMS70C42
TMS32011*
TMS32020
Serial Port
Serial Port
Serial Port
Serial Port
Serial Port
Serial Port
* Requires external hardware
MICROWIRE and MICROWIRE/PLUS are trademarks of
National Semiconductor Corp.