REV. A
AD974
–9–
EXTERNAL DISCONTINUOUS CLOCK DATA READ
DURING CONVERSION WITH NO SYNC OUTPUT
GENERATED
Figure 5 illustrates the method by which data from conversion
“n-1” can be read during conversion “n” while using a discon-
tinuous external clock, without the generation of a SYNC out-
put. After a conversion is initiated, indicated by BUSY going
low, the result of the previous conversion can be read while CS
is low and R/C is high. In this mode CS can be tied low. The
MSB will be valid on the 1st falling edge and the 2nd rising edge of
DATACLK. The LSB will be valid on the 16th falling edge and
the 17th rising edge of DATACLK. A minimum of 16 clock
pulses are required for DATACLK if the receiving device will be
latching data on the falling edge of DATACLK. A minimum of
17 clock pulses are required for DATACLK if the receiving
device will be latching data on the rising edge of DATACLK.
In this mode the data should be clocked out during the first half
of BUSY so not to degrade conversion performance. This re-
quires use of a 10 MHz DATACLK or greater, with data being
read out as soon as the conversion process begins.
EXTERNAL DISCONTINUOUS CLOCK DATA READ
AFTER CONVERSION WITH SYNC OUTPUT GENERATED
Figure 6 illustrates the method by which data from conver-
sion “n” can be read after the conversion is complete using a
discontinuous external clock, with the generation of a SYNC
output. What permits the generation of a SYNC output is a
transition of DATACLK while either CS is high or while both
CS and R/C are low. After a conversion is complete, indicated
by BUSY returning high, the result of that conversion can be
read while CS is Low and R/C is high. In this mode CS can be
tied low. In Figure 6 clock pulse #0 is used to enable the gen-
eration of a SYNC pulse. The SYNC pulse is actually clocked
out approximately 40 ns after the rising edge of clock pulse #1.
The SYNC pulse will be valid on the falling edge of clock pulse
#1 and the rising edge of clock pulse #2. The MSB will be valid
on the falling edge of clock pulse #2 and the rising edge of clock
pulse #3. The LSB will be valid on the falling edge of clock
pulse #17 and the rising edge of clock pulse #18. The advan-
tage of this method of reading data is that it is not being clocked
out during a conversion and therefore conversion performance is
not degraded.
When reading data after the conversion is complete, with the
highest frequency permitted for DATACLK (15.15 MHz), the
maximum possible throughput is approximately 195 kHz and
not the rated 200 kHz.
EXT
DATACLK
R/C
BUSY
SYNC
DATA
0
BIT 15
(MSB)
BIT 14
t
12
t
13
t
14
1 2 15 16
t
15
t
1
t
20
t
2
t
21
t
18
t
18
BIT 0
(LSB)
t
22
Figure 5. Conversion and Read Timing for Reading Previous Conversion Results During a Conversion
Using External Discontinuous Data Clock (EXT/
INT
Set to Logic High,
CS
Set to Logic Low)
EXT
DATACLK
R/C
BUSY
SYNC
DATA
0
t
12
123 18
t
13
t
14
417
t
15
t
15
t
15
t
2
t
17
t
12
t
18
t
18
BIT 15
(MSB)
BIT 14
BIT 0
(LSB)
Figure 6. Conversion and Read Timing Using An External Discontinuous Data Clock
(EXT/
INT
Set to Logic High,
CS
Set to Logic Low)
