ad7450ar-reel7 Analog Devices, Inc., ad7450ar-reel7 Datasheet - Page 19

• Manufacturer Part Number: ad7450ar-reel7
• Description: Differential Input, 1 Msps 12-bit Adc In
  soic-8 And So-8
• Manufacturer: Analog Devices, Inc.

AD7450 to TMS320C5x/C54x
The serial interface on the TMS320C5x/C54x uses a continuous
serial clock and frame synchronization signals to synchronize the
data transfer operations with peripheral devices, such as the
AD7450. The CS input allows easy interfacing between the
TMS320C5x/C54x and the AD7450 with no glue logic required.
The serial port of the TMS320C5x/C54x is set up to operate in
burst mode with internal CLKX (Tx serial clock) and FSX (Tx
frame sync). The serial port control register (SPC) must have
the following setup: FO = 0, FSM = 1, MCM = 1, and
TXM = 1. The format bit, FO, may be set to 1 to set the word
length to 8 bits in order to implement the power-down mode on
the AD7450. The connection diagram is shown in Figure 26. For
signal processing applications, it is imperative that the frame
synchronization signal from the TMS320C5x/C54x provide equi-
distant sampling.
AD7450 to MC68HC16
The serial peripheral interface (SPI) on the MC68HC16 is configured
for master mode (MSTR) = 1, clock polarity bit (CPOL) = 1,
and clock phase bit (CPHA) = 0. The SPI is configured by
writing to the SPI control register (SPCR)—see the 68HC16 user
manual. The serial transfer will take place as a 16-bit operation
when the SIZE bit in the SPCR register is set to SIZE = 1.
To implement the power-down modes with an 8-bit transfer set
SIZE = 0. A connection diagram is shown in Figure 27.
REV. 0
Figure 26. Interfacing to the TMS320C5x/C54x
*
*
ADDITIONAL PINS OMITTED FOR CLARITY
ADDITIONAL PINS OMITTED FOR CLARITY
Figure 27. Interfacing to the MC68HC16
AD7450*
AD7450*
SDATA
SDATA
SCLK
SCLK
CS
CS
TMS320C5x/C54x
CLKX
CLKR
DR
FSX
FSR
SCLK/PMC2
MISO/PMC0
SS/PMC3
MC68HC16
*
*
–19–
AD7450 to DSP56xxx
The connection diagram in Figure 28 shows how the AD7450 can
be connected to the SSI (synchronous serial interface) of the
DSP56xxx family of DSPs from Motorola. The SSI is operated
in synchronous mode (SYN bit in CRB = 1) with internally
generated 1-bit clock period frame sync for both Tx and Rx
(Bits FSL1 = 1 and FSL0 = 0 in CRB). Set the word length to
16 by setting Bits WL1 = 1 and WL0 = 0 in CRA. To imple-
ment the power-down mode on the AD7450, the word length
can be changed to 8 bits by setting its WL1 = 0 and WL0 = 0 in
CRA. It should be noted that for signal processing applica-
tions, it is imperative that the frame synchronization signal
from the DSP56xxx will provide equidistant sampling.
APPLICATION HINTS
Grounding and Layout
The printed circuit board that houses the AD7450 should be
designed so that the analog and digital sections are separated
and confined to certain areas of the board. This facilitates the
use of ground planes that can be easily separated. A minimum
etch technique is generally best for ground planes since it gives
the best shielding. Digital and analog ground planes should be
joined in only one place, and the connection should be a star
ground point established as close to the GND pin on the AD7450
as possible. Avoid running digital lines under the device, as this
will couple noise onto the die. The analog ground plane should
be allowed to run under the AD7450 to avoid noise coupling.
The power supply lines to the AD7450 should use as large a trace
as possible to provide low impedance paths and reduce the effects
of glitches on the power supply line.
Fast switching signals, such as clocks, should be shielded with
digital ground to avoid radiating noise to other sections of the
board, and clock signals should never run near the analog
inputs. Avoid crossover of digital and analog signals. Traces on
opposite sides of the board should run at right angles to each
other. This reduces the effects of feedthrough through the
board. A microstrip technique is by far the best but is not
always possible with a double-sided board.
In this technique, the component side of the board is dedicated
to ground planes, while signals are placed on the solder side.
Good decoupling is also important. All analog supplies should
be decoupled with 10 µF tantalum capacitors in parallel with
0.1 µF capacitors to GND. To achieve the best from these
decoupling components, they must be placed as close as possible
to the device.
*
ADDITIONAL PINS OMITTED FOR CLARITY
Figure 28. Interfacing to the DSP56xxx
AD7450*
SDATA
SCLK
CS
SCLK
SRD
SR2
DSP56xxx
AD7450
*