Datasheet

REV. A
AD974
–10–
EXTERNAL DISCONTINUOUS CLOCK DATA READ
DURING CONVERSION WITH SYNC OUTPUT
GENERATED
Figure 7 illustrates the method by which data from conversion
“n-1” can be read during conversion “n” while using a discon-
tinuous 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. In Figure 7 a conversion is initiated by taking R/C low
with CS tied low. While this condition exists a transition of
DATACLK, clock pulse #0, will enable the generation of a
SYNC pulse. Less then 83 ns after R/C is taken low the BUSY
output will go low to indicate that the conversion process has
begun. Figure 7 shows R/C then going high and after a delay of
greater than 15 ns (t
15
) clock pulse #1 can be taken high to
request the SYNC output. The SYNC output will appear ap-
proximately 40 ns after this rising edge and will be valid on the
falling edge of clock pulse #1 and the rising edge of clock pulse
#2. The MSB will be valid approximately 40 ns after the rising
edge of clock pulse #2 and can be latched off either the falling
edge of clock pulse #2 or 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.
Data should be clocked out during the first half of BUSY to
avoid degrading conversion performance. This requires use of a
10 MHz DATACLK or greater, with data being read out as
soon as the conversion process begins.
t
12
EXT
DATACLK
R/C
BUSY
SYNC
DATA
0
t
13
t
14
t
15
t
15
t
22
t
20
t
1
t
2
t
17
t
12
t
18
t
18
BIT 15
(MSB)
BIT 14
BIT 0
(LSB)
12341718
Figure 7. 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)