參數(shù)資料
型號(hào)： EVAL-AD7877EB
廠商： Analog Devices, Inc.
英文描述： Touch Screen Controller
中文描述： 觸摸屏控制器
文件頁(yè)數(shù)： 20/44頁(yè)
文件大?。?/td> 1002K
代理商： EVAL-AD7877EB
AD7877
CONTROL REGISTERS
Control Register 1 contains the ADC channel address, the
SER/DFR bit (to choose single or differential methods of touch
screen measurement), the register read address, and the ADC
mode bits. Control Register 1 should always be the last register
to be programmed prior to starting conversions. Its power-on
default value is 00h. To change any parameter after conversion
has begun, the part should first be put into mode 00, the
changes made, and then Control Register 1 reprogrammed,
ensuring that it is always the last register to be programmed
before conversions begin.
Rev. A | Page 20 of 44
0
SER/
DFR
CHNL
ADD
3
CHNL
ADD
2
CHNL
ADD
1
CHNL
ADD
0
RD
ADD
4
RD
ADD
3
RD
ADD
2
RD
ADD
1
RD
ADD
0
ADC
MODE
1
ADC
MODE
0
11
0
Figure 34. Control Register 1
Control Register 2 sets the timer, reference, polarity, first
conversion delay, averaging, and acquisition time. Its power-on
default value is 00h. See the Detailed Register Descriptions
section for more information on the control registers.
0
AVG
1
AVG
0
ACQ
1
ACQ
0
PM
1
PM
0
FCD
1
FCD
0
POL
REF
TMR
1
TMR
0
11
0
Figure 35. Control Register 2
CONTROL REGISTER 1
ADC Mode (Control Register 1 Bits <1:0>)
These bits select the operating mode of the ADC. The AD7877
has three operating modes. These are selected by writing to the
mode bits in Control Register 1. If the mode bits are 00, no
conversion is performed.
Table 5. Control Register 1 Mode Selection
Mode 1
Mode 0
Function
0
0
Do not convert (default)
0
1
Single-channel conversion, AD7877 in
slave mode
1
0
Sequence 0, AD7877 in slave mode
1
1
Sequence 1, AD7877 in master mode
If the mode bits are 01, a single conversion is performed on the
channel selected by writing to the channel bits of Control
Register 1 (Bits 7 to 10). At the end of the conversion, if the
TMR bits in Control Register 2 are set to 00, the mode bits
revert to 00 and the ADC returns to no convert mode until a
new conversion is initiated by the host. Setting the TMR bits to
a value other than 00 causes the conversion to be repeated, as
described in the Timer (Control Register 2 Bits <1:0>) section.
The flowchart in Figure 37 shows how the AD7877 operates in
mode 01.
The AD7877 can also be programmed to convert a sequence of
selected channels automatically. The two modes for this type of
conversion are slave mode and master mode.
For slave mode operation, the channels to be digitized are
selected by setting the corresponding bits in Sequencer
Register 0. Conversion is initiated by writing 10b to the mode
bits of Control Register 1. The ADC then digitizes the selected
channels and stores the results in the corresponding results
registers. At the end of the conversion, if the TMR bits in
Control Register 2 are set to 00, the mode bits revert to 00 and
the ADC returns to no convert mode until a new conversion is
initiated by the host. Setting the TMR bits to a code other than
00 causes the conversion sequence to be repeated. The flowchart
in Figure 38 shows how the AD7877 operates in mode 10.
For master mode operation, the channels to be digitized are
written to Sequencer Register 1. Master mode is then selected
by writing 11 to the mode bits in Control Register 1. In this
mode, the wake-up on touch feature is active, so conversion
does not begin immediately. The AD7877 waits until the screen
is touched before beginning the sequence of conversions. The
ADC then digitizes the selected channels, and the results are
written to the results registers. The AD7877 waits for the screen
to be touched again, or for a timer event if the screen remains
touched, before beginning another sequence of conversions.
Figure 39 is a flowchart, showing how the AD7877 operates in
mode 11.
ADC Channel (Control Register 1 Bits <10:7>)
The ADC channel is selected by Bits 10:7 of Control Register 1
(CHADD3 to CHADD0). In addition, the SER/DFR bit, Bit 11,
selects between single-ended and differential conversion. A
complete list of channel addresses is given in Table 6.
For mode 0 (single-channel) conversion, the channel is selected
by writing the appropriate CHADD3 to CHADD0 code to
Control Register 1.
For sequential channel conversion, channels to be converted are
selected by setting bits corresponding to the channel number in
Sequencer Register 1 for slave mode sequencing or Sequencer
Register 2 for master mode sequencing.
For both single-channel and sequential conversion, normal
(single-ended) conversion is selected by clearing the SER/DFR
bit in Control Register 1. Ratiometric (differential) conversion is
selected by setting the SER/DFR bit.
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