Datasheet

68HC11
DAC108S085
PC7
SCK
MOSI
SCLK
DIN
SYNC
80C51/80L51
DAC108S085
P3.3
TXD
RXD
SCLK
DIN
SYNC
ADSP-2101/
ADSP2103
DAC108S085
TFS
DT
SCLK
DIN
SCLK
SYNC
DAC108S085
www.ti.com SNAS423B –AUGUST 2007–REVISED MARCH 2013
DSP/MICROPROCESSOR INTERFACING
Interfacing the DAC108S085 to microprocessors and DSPs is quite simple. The following guidelines are offered
to hasten the design process.
ADSP-2101/ADSP2103 Interfacing
Figure 41 shows a serial interface between the DAC108S085 and the ADSP-2101/ADSP2103. The DSP should
be set to operate in the SPORT Transmit Alternate Framing Mode. It is programmed through the SPORT control
register and should be configured for Internal Clock Operation, Active Low Framing and 16-bit Word Length.
Transmission is started by writing a word to the Tx register after the SPORT mode has been enabled.
Figure 41. ADSP-2101/2103 Interface
80C51/80L51 Interface
A serial interface between the DAC108S085 and the 80C51/80L51 microcontroller is shown in Figure 42. The
SYNC signal comes from a bit-programmable pin on the microcontroller. The example shown here uses port line
P3.3. This line is taken low when data is transmitted to the DAC108S085. Since the 80C51/80L51 transmits 8-bit
bytes, only eight falling clock edges occur in the transmit cycle. To load data into the DAC, the P3.3 line must be
left low after the first eight bits are transmitted. A second write cycle is initiated to transmit the second byte of
data, after which port line P3.3 is brought high. The 80C51/80L51 transmit routine must recognize that the
80C51/80L51 transmits data with the LSB first while the DAC108S085 requires data with the MSB first.
Figure 42. 80C51/80L51 Interface
68HC11 Interface
A serial interface between the DAC108S085 and the 68HC11 microcontroller is shown in Figure 43. The SYNC
line of the DAC108S085 is driven from a port line (PC7 in the figure), similar to the 80C51/80L51.
The 68HC11 should be configured with its CPOL bit as a zero and its CPHA bit as a one. This configuration
causes data on the MOSI output to be valid on the falling edge of SCLK. PC7 is taken low to transmit data to the
DAC. The 68HC11 transmits data in 8-bit bytes with eight falling clock edges. Data is transmitted with the MSB
first. PC7 must remain low after the first eight bits are transferred. A second write cycle is initiated to transmit the
second byte of data to the DAC, after which PC7 should be raised to end the write sequence.
Figure 43. 68HC11 Interface
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