EVAL-CONTROLBOARD AD [Analog Devices], EVAL-CONTROLBOARD Datasheet - Page 18

• Manufacturer Part Number: EVAL-CONTROLBOARD
• Description: 16-Bit, 100 kSPS CMOS ADC
• Manufacturer: AD [Analog Devices]

AD7660
MICROPROCESSOR INTERFACING
The AD7660 is ideally suited for traditional dc measurement
applications supporting a microprocessor, and ac signal pro-
cessing applications interfacing to a digital signal processor.
The AD7660 is designed to interface either with a parallel 16-
bit-wide interface or with a general purpose serial port or I/O
ports on a microcontroller. A variety of external buffers can be
used with the AD7660 to prevent digital noise from coupling
into the ADC. The following sections illustrate the use of the
AD7660 with an SPI equipped microcontroller, the ADSP-
21065L and ADSP-218x signal processors.
SPI Interface (MC68HC11)
Figure 21 shows an interface diagram between the AD7660 and
an SPI-equipped microcontroller like the MC68HC11. To
accommodate the slower speed of the microcontroller, the
AD7660 acts as a slave device and data must be read after
conversion. This mode also allows the “daisy chain” feature.
The convert command could be initiated in response to an
internal timer interrupt. The reading of output data, one byte
at a time, if necessary, could be initiated in response to the
end-of-conversion signal (BUSY going low) using an interrupt
line of the microcontroller. The Serial Peripheral Interface (SPI)
on the MC68HC11 is configured for master mode (MSTR) = 1,
Clock Polarity Bit (CPOL) = 0, Clock Phase Bit (CPHA) = 1
and SPI interrupt enable (SPIE) = 1 by writing to the SPI Control
Register (SPCR). The IRQ is configured for edge-sensitive-only
operation (IRQE = 1 in OPTION register).
OVDD
DVDD
SER/PAR
EXT/INT
CS
RD
INVSCLK
AD7660
ADDITIONAL PINS OMITTED FOR CLARITY
SDOUT
CS, RD
CNVST
BUSY
SDOUT
SCLK
CNVST
BUSY
SCLK
t
16
t
3
t
31
X
IRQ
MISO/SDI
SCK
I/O PORT
t
36
1
t
MC68HC11
35
D15
t
37
2
D14
t
32
EXT/INT = 1
3
D13
ADSP-21065L in Master Serial Interface
As shown in Figure 22, the AD7660 can be interfaced to the
ADSP-21065L using the serial interface in master mode with-
out any glue logic required. This mode combines the advantages
to reduce the wire connections and to be able to read the data
during or after conversion at user convenience.
The AD7660 is configured for the internal clock mode (EXT/INT
low) and acts, therefore, as the master device. The convert com-
mand can be generated by either an external low jitter oscillator
or, as shown, by a FLAG output of the ADSP-21065L or by a
frame output TFS of one serial port of the ADSP-21065L which
can be used like a timer. The serial port on the ADSP-21065L is
configured for external clock (IRFS = 0), rising edge active
(CKRE = 1), external late framed sync signals (IRFS = 0,
LAFS = 1, RFSR = 1) and active high (LRFS = 0). The serial
port of the ADSP-21065L is configured by writing to its receive
control register (SRCTL)—see ADSP-2106x SHARC User’s
Manual. Because the serial port, within the ADSP-21065L will
be seeing a discontinuous clock, an initial word reading has to
be done after the ADSP-21065L has been reset to ensure that
the serial port is properly synchronized to this clock during each
following data read operation.
OVDD
OGND
OR
DVDD
INVSCLK = 0
14
CS
INVSCLK
INVSYNC
SER/PAR
RDC/SDIN
RD
EXT/INT
15
AD7660
ADDITIONAL PINS OMITTED FOR CLARITY
D1
SDOUT
CNVST
16
SYNC
SCLK
D0
RFS
DR
RCLK
FLAG OR TFS
ADSP-21065L
SHARC