19
®
ADS7807
The monostable multi-vibrator in this circuit will provide
varying pulse widths for the convert pulse. The pulse
width will be determined by the external R and C values
used with the multi-vibrator. The 74HCT123N data sheet
shows that the pulse width is (0.7) RC. Choosing a pulse
FIGURE 16. DSP56000 Interface to the ADS7807.
R/C
BUSY
SDATA
DATACLK
CS
EXT/INT
BYTE
ADS7807
SC1
SRD
SCO
DSP56000
SYN = 0 (Asychronous)
GCK = 1 (Gated clock)
SCD1 = 0 (SC1 is an input)
SHFD = 0 (Shift MSB first)
WL1 = 1 WL0 = 0 (Word length = 16 bits)
Convert Pulse
width as close to the minimum value specified in this data
sheet will offer the best performance. See the Starting A
Conversion section of this data sheet for details on the
conversion pulse width.
The maximum conversion rate for a 20.48MHz DSP56000
is exactly 40kHz. Note that this will not be the case for
the ADS7806. See the ADS7806 data sheet for more
information.
FIGURE 17. DSP56000 Interface to the ADS7807. Processor Initiates Conversions.
R
EXT1
C
EXT1
Q1
B1
CLR1
A1
R/C
DATACLK
SDATA
CS
EXT/INT
BYTE
ADS7807
74HCT123N
SC2
SC0
SRD
DSP56000
SYN = 0 (Asychronous)
GCK = 1 (Gated clock)
SCD2 = 1 (SC2 is an output)
SHFD = 0 (Shift MSB first)
WL1 = 1 WL0 = 0 (Word length = 16 bits)
R
+5V
C
+5V
