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參數(shù)資料
| 型號(hào)： | ADN2850ACP25-RL7 |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 數(shù)字電位計(jì) |
| 英文描述： | Nonvolatile Memory, Dual 1024 Position Programmable Resistors |
| 中文描述： | DUAL 25K DIGITAL POTENTIOMETER, 3-WIRE SERIAL CONTROL INTERFACE, 1024 POSITIONS, QCC16 |
| 封裝： | 5 X 5 MM, LFCSP-16 |
| 文件頁(yè)數(shù)： | 8/18頁(yè) |
| 文件大?。?/td> | 270K |
| 代理商： | ADN2850ACP25-RL7 |
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PRELIMINARY TECHNICAL DATA
Nonvolatile Memory Programmable Resistors
ADN2850
REV PrH, 13, AUG 2001
8
OPERATIONAL OVERVIEW
The ADN2850 programmable resistor is designed to operate as a
true variable resistor. The resistor wiper position is determined
by the RDAC register contents. The RDAC register acts as a
scratch pad register which allows unlimited changes of
resistance settings. The scratch pad register can be programmed
with any position setting using the standard SPI serial interface
by loading the 24-bit data word. The format of the data word is
that the first 4 bits are instructions, the following 4 bits are
Addresses, and the last 16 bits are data. Once a specific value is
set, this value can be saved into a corresponding EEMEM
register. During subsequent power up, the wiper setting will
automatically be loaded at that value. Saving data to the
EEMEM takes about 25ms, and consumes approximately 20mA.
During this time the shift register is locked preventing any
changes from taking place. The RDY pin indicates the
completion of this EEMEM saving process. There are also 13, 2
bytes each of user defined data that can be stored in EEMEM.
OPERATION DETAIL
There are sixteen instructions which faciliates users’
programming needs. Refer to Table 2, the instructions are:
0. Do Nothing
1.
Restore EEMEM setting to RDAC
2.
Save RDAC setting to EEMEM
3.
Save RDAC setting or user data to EEMEM
4.
Decrement 6dB
5.
Decrement all 6dB
6.
Decrement one step
7.
Decrement all one step
8.
Reset EEMEM setting to RDAC
9.
Read EEMEM to SDO
10.
Read Wiper Setting to SDO
11.
Write data to RDAC
12.
Increment 6dB
13.
Increment all 6dB
14.
Increment one step
15.
Increment all one step
Scratch Pad and EEMEM Programming
The basic mode of setting the programmable resistor wiper
position (programming the scratch pad register) is accomplished
by loading the serial data input register with the instruction #11,
the correponding address, and the data. When the desired wiper
position is determined, the user can load the serial data input
register with the instruction #2, which stores the setting into the
corresponding EEMEM register. After 25ms the wiper position
will be stored in the corresponding EEMEM location. If desired,
this value can be changed by users in the future or users can set
the write-protect to permanently protect the data. Figure 3
provides a programming example listing the sequence of serial
data input (SDI) words and the corresponding serial data output
(SDO) in hexadecimal format.
SDI
SDO
Action
B00100
H
XXXXXX
H
Loads data 100
H
into RDAC1 register, Wiper
W1 moves to 1/4 full-scale position
20xxxx
H
B00100
H
Saves copy of RDAC1 register contents into
corresponding EEMEM1 register.
B10200
H
20xxxx
H
Loads 200
H
data into RDAC2 register, Wiper
W2 moves to 1/2 full-scale position
21xxxx
H
B10200
H
Saves copy of RDAC2 register contents into
corresponding EEMEM2 register.
Figure 3. Set and Save two channels of programmable resistors
with independent datas.
At system power ON, the scratch pad register is refreshed with
the value previously saved in the corresponding EEMEM
register. The factory preset EEMEM value is midscale. The
scratch pad register can also be loaded with the contents of the
EEMEM register in three different ways. Executing instruction
#1 retrieves the corresponding EEMEM value, executing
instruction #8 resets both channels EEMEM values, and pulsing
the
PR
pin also refreshs both EEMEM settings. Operate the
PR
function however requires a complete pulse signal. When
PR
goes low, the internal logic sets the wiper at midscale. The
EEMEM value will not be loaded until
PR
returns to high
.
E2MEM Protection
The write-protect (
WP
) pin provides a hardware EEMEM
protection feature which disables any changes of the current
content in the scratch pad register at all except commands 1, 8,
and
PR
. Executing these three events cause the EEMEM values
restored to the scratch pad registers.
Linear Increment and Decrement Commands
The increment and decrement commands (#14, #15, #6, #7) are
useful for linear step adjustment applications. These commands
simplify micro controller software coding by allowing the
controller to just send an increment or decrement command to
the device. The adjustment can be individual or ganged
arrangement. For increment command, executing instruction
#14 will automatically move the wiper to the next resistance
segment position. The master increment instruction #15 will
move all resistor wipers up by one position.
Logarithmic Taper Mode Adjustment (±6dB/step)
Four programming instructions produce logarithmic taper
increment and decrement wiper position control by either
individual or ganged arrangement. These settings are activated
by the 6dB increment and 6dB decrement instructions #12 &
#13 and #4 & #5 respectively. For example, starting at zero
scale, executing eleven times of the increment instruction #12
will move the wiper in +6B per step from the 0% of the full
scale R
WB
to the full scale R
WB
. The +6dB increment instruction
doubles the value of the RDAC register contents each time the
command is executed. When the wiper position is near the
maximum setting, the last +6dB increment instruction will cause
the wiper to go to the full-scale 1023 code position. Further
+6dB per increment instruction will no longer change the wiper
position beyond its full scale.
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