Datasheet

Data Sheet AD7952
Rev. A | Page 29 of 32
HARDWARE CONFIGURATION
The AD7952 can be configured at any time with the dedicated
hardware pins WARP, IMPULSE, BIPOLAR, TEN, OB/
2C
, and
PD for parallel mode (SER/
PAR
= low) or serial hardware mode
(SER/
PAR
= high, HW/
SW
= high). Programming the AD7952
for mode selection and input range configuration can be done
before or during conversion. Like the RESET input, the ADC
requires at least one acquisition time to settle, as shown in
Figure 45. See Table 6 for pin descriptions. Note that these
inputs are high impedance when using the software
configuration mode.
SOFTWARE CONFIGURATION
The pins multiplexed on D[13:10] used for software configura-
tion are: HW/
SW
, SCIN, SCCLK, and
SCCS
. The AD7952 is
programmed using the dedicated write-only serial configurable
port (SCP) for conversion mode, input range selection, output
coding, and power-down using the serial configuration register.
See Table 10 for details of each bit in the configuration register.
The SCP can only be used in serial software mode selected with
SER/
PAR
= high and HW/
SW
= low because the port is
multiplexed on the parallel interface.
The SCP is accessed by asserting the port’s chip select,
SCCS
,
and then writing SCIN synchronized with SCCLK, which (like
SDCLK) is edge sensitive depending on the state of INVSCLK.
See Figure 46 for timing details. SCIN is clocked into the con-
figuration register MSB first. The configuration register is an
internal shift register that begins with Bit 8, the START bit. The
9
th
SPPCLK edge updates the register and allows the new settings to
be used. As indicated in the timing diagram, at least one acquisition
time is required from the 9
th
SCCLK edge. Bits [1:0] are reserved
bits and are not written to while the SCP is being updated.
The SCP can be written to at any time, up to 40 MHz, and it is
recommended to write to while the AD7952 is not busy
converting, as detailed in Figure 46. In this mode, the full
1 MSPS is not attainable because the time required for SCP access
is (t
31
+ 9 × 1/SCCLK + t
8
) minimum. If the full throughput is
required, the SCP can be written to during conversion; however,
it is not recommended to write to the SCP during the last 450 ns
of conversion (BUSY = high), or performance degradation can
result. In addition, the SCP can be accessed in both serial master
and serial slave read during and read after convert modes.
Note that at power-up, the configuration register is undefined.
The RESET input clears the configuration register (sets all bits
to 0), thus placing the configuration to 0 V to 5 V input, normal
mode, and twos complemented output.
Table 10. Configuration Register Description
Bit Name Description
8 START
START bit. With the SCP enabled (
SCCS
= low),
when START is high, the first rising edge of SCCLK
(INVSCLK = low) begins to load the register with the
new configuration.
7 BIPOLAR Input Range Select. Used in conjunction with Bit 6,
TEN, per the following.
Input Range (V) BIPOLAR TEN
0 to 5 Low Low
0 to 10 Low High
±5 High Low
±10 High High
6 TEN Input Range Select. See Bit 7, BIPOLAR.
5 PD Power Down.
PD = low, normal operation.
PD = high, power down the ADC. The SCP is
accessible while in power-down. To power-up
the ADC, write PD = low on the next configuration
setting.
4 IMPULSE
Mode Select. Used in conjunction with Bit 3, WARP,
per the following.
Mode WARP IMPULSE
Normal Low Low
Impulse Low High
Warp High Low
Normal High High
3 WARP Mode Select. See Bit 4, IMPULSE.
2
OB/
2C
Output Coding.
OB/
2C
= low, use twos complement output.
OB/
2C
= high, use straight binary output.
1 RSV Reserved.
0 RSV Reserved.
WARP,
IMPULSE
BUSY
HW/SW = 0
CNVST
BIPOLAR,
TEN
t
8
SER/PAR = 0, 1PD = 0
t
8
0
6589-044
Figure 45. Hardware Configuration Timing