Datasheet

Data Sheet AD7699
Rev. | Page 23 of 28
READ/WRITE SPANNING CONVERSION WITHOUT
A BUSY INDICATOR
This mode is used when the AD7699 is connected to any host
using an SPI, serial port, or FPGA. The connection diagram is
shown in Figure 36, and the corresponding timing is given in
Figure 37. For SPI, the host should use CPHA = CPOL = 0.
Reading/writing spanning conversion is shown, which covers
all three modes detailed in the Digital Interface section. For this
mode, the host must generate the data transfer based on the
conversion time. For an interrupt driven transfer, refer to the
next section, which uses a busy indicator.
A rising edge on CNV initiates a conversion, forces SDO to
high impedance, and ignores data present on DIN. After a
conversion is initiated, it continues until completion irrespective
of the state of CNV. CNV must be returned high before the safe
data transfer time, t
DATA
, and then held high beyond the conver-
sion time, t
CONV
, to avoid generation of the busy signal indicator.
After the conversion is complete, the AD7699 enters the acquisi-
tion phase and powers down. When the host brings CNV low
after t
CONV
(max), the MSB is enabled on SDO. The host also
must enable the MSB of CFG at this time (if necessary) to begin
the CFG update. While CNV is low, both a CFG update and a
data readback take place. The first 14 SCK rising edges are used
to update the CFG, and the first 15 SCK falling edges clock out
the conversion results starting with MSB − 1. The restriction
for both configuring and reading is that they both must occur
before the t
DATA
time of the next conversion elapses. All 14 bits
of CFG[13:0] must be written, or they are ignored. In addition,
if the 16-bit conversion result is not read back before t
DATA
elapses,
it is lost.
The SDO data is valid on both SCK edges. Although the rising
edge can be used to capture the data, a digital host using the
SCK falling edge allows a faster reading rate, provided it has an
acceptable hold time. After the 16
th
(or 30
th
) SCK falling edge, or
when CNV goes high (whichever occurs first), SDO returns to
high impedance.
If CFG readback is enabled, the CFG associated with the conver-
sion result is read back MSB first following the LSB of the
conversion result. A total of 30 SCK falling edges is required to
return SDO to high impedance if this is enabled.
MISO
MOSI
SCK
SS
CNV
FOR SPI USE CPHA = 0, CPOL = 0.
SCK
SDO
DIN
AD7699
DIGITAL HOST
07354-034
Figure 36. Connection Diagram for the AD7699 Without a Busy Indicator
UPDATE (n)
CFG/SDO
UPDATE (n + 1)
CFG/SDO
ACQUISITION (n)
ACQUISITION
(n + 1)
ACQUISITION
(n – 1)
MSB MSB – 1
1
2
BEGIN DATA (n – 1)
BEGIN CFG (n + 1)
CFG
MSB
CFG
MSB – 1
LSB + 1
14
15
SEE NOTE
SEE NOTE
NOTES
1. THE LSB IS FOR CONVERSION RESULTS OR THE CONFIGURATION REGISTER CFG (n – 1) IF.
15 SCK FALLING EDGES = LSB OF CONVERSION RESULTS.
29 SCK FALLING EDGES = LSB OF CONFIGURATION REGISTER.
ON THE 16TH OR 30TH SCK FALLING EDGE, SDO IS DRIVEN TO HIGH IMPENDANCE.
16/
30
CONVERSION (n)
RETURN CNV HIGH
FOR NO BUSY
END DATA (n – 1)
END CFG (n + 1)
CFG
LSB
X
X
> t
CONV
LSB
SCK
CNV
DIN
SDO
LSB + 1
14
15
16/
30
CONVERSION (n – 1)
RETURN CNV HIGH
FOR NO BUSY
END DATA (n – 2)
END CFG (n)
CFG
LSB
X
X
t
CONV
t
DATA
t
CNVH
t
DATA
t
DIS
t
DIS
t
EN
t
DSDO
t
HSDO
t
HDIN
t
SDIN
t
CLSCK
t
EN
t
EN
t
SCK
t
SCKH
t
SCKL
t
DIS
t
DIS
t
CONV
LSB
07354-035
t
ACQ
t
CYC
(QUIET
TIME)
(QUIET
TIME)
Figure 37. Serial Interface Timing for the AD7699 Without a Busy Indicator
B