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參數(shù)資料
| 型號： | AD7866 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Dual 1 MSPS, 12-Bit, 2-Channel SAR ADC with Serial Interface |
| 中文描述： | 雙1 MSPS的12位，雙通道SAR型ADC的串行接口 |
| 文件頁數(shù)： | 19/20頁 |
| 文件大小： | 304K |
| 代理商： | AD7866 |
REV. 0
AD7866
–19–
For example, if the ADSP-2189 had a 20 MHz crystal, such that
it had a master clock frequency of 40 MHz then the master cycle
time would be 25 ns. If the SCLKDIV register is loaded with
the value 3, a SCLK of 5 MHz is obtained, and eight master
clock periods will elapse for every 1 SCLK period. Depending
on the throughput rate selected, if the timer register was loaded
with the value, say 803, (803 + 1 = 804) 100.5 SCLKs will occur
between interrupts and subsequently between transmit instructions.
This situation will result in non-equidistant sampling as the
transmit instruction is occurring on a SCLK edge. If the number
of SCLKs between interrupts is a whole integer figure of N,
equidistant sampling will be implemented by the DSP.
AD7866
*
V
DRIVE
D
OUT
A
D
OUT
B
CS
SCLK
ADSP-21xx
*
DR0
DR1
TFS0
SCLK0
RFS0
RSF1
SCLK1
ADDITIONAL PINS OMITTED
FOR CLARITY
V
DD
Figure 24. Interfacing the AD7866 to the ADSP-218x
AD7866
*
V
DRIVE
D
OUT
A
D
OUT
B
CS
SCLK
TMS320C541
*
DR0
DR1
CLKX0
CLKR0
CLKX1
CLKR1
*
ADDITIONAL PINS OMITTED
FOR CLARITY
V
DD
FSX0
FSR0
FSR1
Figure 25. Interfacing the AD7866 to the TMS320C541
AD7866 to TMS320C541
The serial interface on the TMS320C541 uses a continuous serial
clock and frame synchronization signals to synchronize the data
transfer operations with peripheral devices like the AD7866. The
CS
input allows easy interfacing between the TMS320C541 and
the AD7866 without any glue logic required. The serial ports of
the TMS320C541 are set up to operate in burst mode with internal
CLKX (Tx serial clock on serial port 0) and FSX0 (Tx frame
sync from serial port 0). The serial port control registers (SPC)
must have the following setup:
SPC0: FO = 0, FSM = 1, MCM = 1 and TxM = 1
SPC1: FO = 0, FSM = 1, MCM = 0 and TxM = 0
The format bit, FO, may be set to 1 to set the word length to 8 bits,
in order to implement the power-down modes on the AD7866.
The connection diagram is shown in Figure 25. It should be
noted that for signal processing applications, it is imperative
that the frame synchronization signal from the TMS320C541
will provide equidistant sampling. The V
DRIVE
pin of the AD7866
takes the same supply voltage as that of the TMS320C541. This
allows the ADC to operate at a higher voltage than the serial
interface, i.e., TMS320C541, if necessary.
AD7866 to DSP-563xx
The connection diagram in Figure 26 shows how the AD7866
can be connected to the ESSI (Synchronous Serial Interface) of the
DSP-563xx family of DSPs from Motorola. Each ESSI (two on-board)
is operated in Synchronous Mode (Bit SYN = 1 in CRB register)
with internally generated word length frame sync for both Tx and
Rx (bits FSL1 = 0 and FSL0 = 0 in CRB). Normal operation
of the ESSI is selected by making MOD = 0 in the CRB. Set the
word length to 16 by setting bits WL1 = 1 and WL0 = 0 in CRA.
To implement the power-down modes on the AD7866 the
word length can be changed to eight bits by setting bits WL1 = 0
and WL0 = 0 in CRA. The FSP Bit in the CRB should be set to 1
so the frame sync is negative. It should be noted that for signal pro-
cessing applications, it is imperative that the frame synchronization
signal from the DSP-563xx will provide equidistant sampling.
In the example shown in Figure 26, the serial clock is taken from
the ESSI0 so the SCK0 pin must be set as an output, SCKD = 1,
while the SCK1 pin is set up as an input, SCKD = 0. The frame
sync signal is taken from SC02 on ESSI0, so SCD2 = 1, while
on ESSI1, SCD2 = 0 so SC12 is configured as an input. The
V
DRIVE
pin of the AD7866 takes the same supply voltage as that
of the DSP-563xx. This allows the ADC to operate at a higher
voltage than the serial interface, i.e., DSP-563xx, if necessary.
AD7866
*
V
DRIVE
D
OUT
A
D
OUT
B
CS
SCLK
DSP-563xx
*
SC02
SC12
SCK0
SRD0
SRD1
SCK1
*
ADDITIONAL PINS OMITTED
FOR CLARITY
V
DD
Figure 26. Interfacing to the DSP-563xx
APPLICATION HINTS
Grounding and Layout
The analog and digital supplies to the AD7866 are independent
and separately pinned out to minimize coupling between the analog
and digital sections of the device. The AD7866 has very good
immunity to noise on the power supplies as can be seen by the
PSRR vs. Supply Ripple Frequency plots, TPC 3a – TPC4b.
However, care should still be taken with regard to grounding
and layout.
The printed circuit board that houses the AD7866 should be de-
signed such 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 as it gives the best
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