AD7853 Analog Devices, AD7853 Datasheet - Page 23

• Manufacturer Part Number: AD7853
• Description: 3 V to 5 V Single Supply, 200 kSPS, 12-Bit, Serial Sampling ADC
• Manufacturer: Analog Devices

Specifications of AD7853

• Resolution (bits): 12bit
• # Chan: 1
• Sample Rate: 200kSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni,SE-Uni
• Ain Range: (Vref) p-p,Uni (Vref)
• Adc Architecture: SAR
• Pkg Type: DIP,SOIC

REV. B
SERIAL INTERFACE SUMMARY
Table IX details the five interface modes and the serial clock
edges from which the data is clocked out by the AD7853/
AD7853L (DOUT Edge) and that the data is latched in on
(DIN Edge). The logic level of the POLARITY pin is shown
and it is clear that this reverses the edges.
In Interface Modes 4 and 5 the SYNC always clocks out the
first data bit and SCLK will clock out the subsequent bits.
In Interface Modes 1, 2, and 3 the SYNC is gated with the
SCLK and the POLARITY pin. Thus the SYNC may clock out
the MSB of data. Subsequent bits will be clocked out by the
serial clock, SCLK. The conditions for the SYNC clocking out
the MSB of data is as follows:
With the POLARITY pin high the falling edge of SYNC will clock
out the MSB if the serial clock is low when the SYNC goes low.
With the POLARITY pin low the falling edge of SYNC will clock
out the MSB if the serial clock is high when the SYNC goes low.
Interface
Mode
1, 2, 3
4, 5
Resetting the Serial Interface
When writing to the part via the DIN line there is the possibility
of writing data into the incorrect registers, such as the test regis-
ter for instance, or writing the incorrect data and corrupting the
serial interface. The SYNC pin acts as a reset. Bringing the
SYNC pin high resets the internal shift register. The first data
bit after the next SYNC falling edge will now be the first bit of a
new 16-bit transfer. It is also possible that the test register con-
tents were altered when the interface was lost. Therefore, once
the serial interface is reset, it may be necessary to write the 16-
bit word 0100 0000 0000 0010 to restore the test register to its
default value. Now the part and serial interface are completely
reset. It is always useful to retain the ability to program the
SYNC line from a port of the Controller/DSP to have the
ability to reset the serial interface.
Table X summarizes the interface modes provided by the
AD7853/AD7853L. It also outlines the various P/ C to which
the particular interface is suited.
The interface mode is determined by the serial mode selection
pins SM1 and SM2. Interface Mode 2 is the default mode. Note
that Interface Mode 1 and 2 have the same combination of SM1
and SM2. Interface Mode 1 may only be set by programming
the control register (see section on control register). External
Table IX. SCLK Active Edge for Different Interface Modes
POLARITY
Pin
0
1
0
1
DOUT
SCLK
SCLK
SCLK
Edge
SCLK
DIN
Edge
SCLK
SCLK
SCLK
SCLK
–23–
SCLK and SYNC signals (SYNC may be hardwired low) are
required for Interfaces Modes 1, 2, and 3. In Interface Modes 4
and 5, the AD7853/AD7853L generates the SCLK and SYNC.
Some of the more popular Processors, Controllers, and the
DSP machines that the AD7853/AD7853L will interface to
directly are mentioned here. This does not cover all Cs, Ps
and DSPs. The interface mode of the AD7853/AD7853L that is
mentioned here for a specific C, P, or DSP is only a guide
and in most cases another interface mode may work just as well.
A more detailed timing description on each of the interface
modes follows.
SM1
Pin
0
0
0
1
1
SM2
Pin
0
0
1
0
1
Table X. Interface Mode Description
8XC51
8XL51
PIC17C42
68HC11
68L11
68HC16
PIC16C64
ADSP-21xx
DSP56000
DSP56001
DSP56002
DSP56L002
TMS320C30
68HC16
ADSP-21xx
DSP56000
DSP56001
DSP56002
DSP56L002
TMS320C20
TMS320C25
TMS320C30
TMS320C5x
TMS320LC5x
Processor/
Controller
AD7853/AD7853L
Interface
Mode
1 (2-Wire)
(DIN is an Input/
Output pin)
2 (3-Wire, SPI/QSPI)
(Default Mode)
3 (QSPI)
(External Serial
Clock, SCLK, and
External Frame Sync,
SYNC, are required)
4 (DSP is Slave)
(AD7853/AD7853L
generates a
noncontinuous
[16 clocks] Serial
Clock, SCLK, and the
Frame Sync, SYNC)
5 (DSP is Slave)
(AD7853/AD7853L
generates a
continuous Serial
Clock, SCLK, and the
Frame Sync, SYNC)