Datasheet

33
LTC2404/LTC2408
APPLICATIONS INFORMATION
WUU
U
Figure 30. LTC2408/LTC1391-684C11 MCU Digital Interface Routine
ENLWMX TBA Restore contents of Accum. A
ORAA #$08 Set the MUX’s ENABLE bit
MUXSPI STAA SPDR Transfer Accum. A contents to SPI register to initiate
* serial transfer
WAITMUX LDAA SPSR Get SPI transfer status
BPL WAITMUX If the transfer is not finished, read status
*
***************************************
* Enable the LTC2408 *
***************************************
*
BCLR PORTD,Y %00100000 This sets the SS* output bit to a logic
* low, selecting the LTC2408
*
***************************************
* The next short loop waits for the *
* LTC2408’s conversion to finish before *
* starting the SPI data transfer *
***************************************
*
CONVEND LDAA PORTD Retrieve the contents of port D
ANDA #%00000100 Look at bit 2
* Bit 2 = Hi; the LTC2408’s conversion is not
* complete
* Bit 2 = Lo; the LTC2408’s conversion is complete
BNE CONVEND Branch to the loop’s beginning while bit 2 remains
* high
*
***************************************
* The SPI data transfer *
***************************************
*
TRFLP1 LDAA #$0 Load accumulator A with a null byte for SPI transfer
STAA SPDR This writes the byte into the SPI data register and
* starts the transfer
WAIT1 LDAA SPSR This loop waits for the SPI to complete a serial
* transfer/exchange by reading the SPI Status Register
BPL WAIT1 The SPIF (SPI transfer complete flag) bit is the SPSR’s
* MSB and is set to one at the end of an SPI transfer. The
* branch will occur while SPIF is a zero.
LDAA SPDR Load accumulator A with the current byte of LTC2408 data
* that was just received
STAA 0,X Transfer the LTC2408’s data to memory
INX Increment the pointer
CPX #DIN4+1 Has the last byte been transferred/exchanged?
BNE TRFLP1 If the last byte has not been reached, then proceed to
* the next byte for transfer/exchage
BSET PORTD,Y %00100000 This sets the SS* output bit to a logic
* high, de-selecting the LTC2408
PULA Restore the A register
PULY Restore the Y register
PULX Restore the X register
RTS
An 8-Channel DC-to-Daylight Digitizer
The circuit in Figure 31 shows an example of the LTC2408’s
flexibility in digitizing a number of real-world physical
phenomena—from DC voltages to ultraviolet light. All of
the examples implement single-ended signal condition-
ing. Although differential signal conditioning is a preferred
approach in applications where the sensor is a bridge-
type, is located some distance from the ADC or operates
in a high ambient noise environment, the LTC2408’s low
power dissipation allows circuit operation in close prox-
imity to the sensor. As a result, conditioning the sensor
output can be greatly simplified through the use of single-
ended arrangements. In those applications where differ-
ential signal conditioning is required, chopper