MAX11800 Datasheet, PDF (23/56 Pages) Maxim Integrated Products – Low-Power, Ultra-Small Resistive Touch-Screen Controllers with I2C/SPI Interface

Low-Power, Ultra-Small Resistive Touch-Screen
Controllers with I²C/SPI Interface
Combined Commands
Combined commands reduce AP interaction with the
MAX11800–MAX11803 by allowing multiple measure-
ments. For example, the MAX11800–MAX11803 can be
instructed to provide X and Y data, or X and Y and Z1
data, or X and Y and Z1 and Z2 data using a single
command.
Data Tagging
In direct conversion modes, all measurement data is
contained in a 16-bit word. X, Y, Z1, and Z2 information
is logged independently. Each word consists of 12 bits
of measurement data plus a 2-bit measurement type
(MTAG) and a 2-bit event tag (ETAG). The measure-
ment tag identifies whether the data represents an X, Y,
Z1, or Z2 result. The event tag indicates the point at
which the data is sampled (initial, midpress, or release)
during the touch event. When trying to read a result
which is pending an update, the entire data stream is
read back as FFFFh and the event tag as 11b, indicat-
ing that the corresponding measurement is in progress
and that the data stream is to be ignored. For com-
bined commands, all data locations requested by the
command are marked FFFFh, pending the completion
of the entire command and the proper tagging of the
data. See Table 5.
Direct conversion modes do not use the internal FIFO
or support the aperture (see the Aperture Modes and
Options section) function. Each measurement type is
afforded a single location in the memory. The AP must
retrieve the data from the last requested measurement
before moving on to the next measurement of the type.
Auxiliary measurement data is not tagged because it is
not related to panel operation. Auxiliary measurement
data is stored and read back identically to the other
direct conversion data. The tag locations for auxiliary
measurement data are always set to 0000b, unless the
read occurs when an auxiliary measurement is in
progress. In this situation, the tag locations read 1111b
and the data stream reads back FFFFh.
Low-Power Modes
There are also two low-power modes, LPM and TDM.
During LPM, all circuitry is off, including the on-chip
touch-detect pullup resistors used in the touch-detect
circuitry. In direct conversion modes, a user-request ini-
tiates the next operation and all circuitry is off until a
user-command is received. Therefore, the current con-
sumption is primarily due to junction leakage. In
autonomous conversion mode, an on-chip oscillator
and timer are constantly running. Therefore, the device
current consumption is primarily determined by the
oscillator and timer. During TDM, all circuitry is off
except the on-chip pullup resistor. This is an untimed
mode (oscillator and timer are off) for both ACM and
DCM (no digital current). This mode only consumes
current through the on-chip pullup resistor when a
touch is present.
Table 4. Median Averaging Operations
AVERAGING MODE
NUMBER OF
SAMPLES TAKEN
NUMBER OF HIGH
SAMPLES REMOVED
1
4
1
2
8
2
3
16
4
NUMBER OF LOW
SAMPLES REMOVED
1
2
4
NUMBER OF
REMAINING SAMPLES
AVERAGED
2
4
8
Table 5. Data Word Structure (All Direct Conversion Modes)
INDEX
15 14 13 12 11 10 9
8
7
6
5
4
3
2
Byte
MSB Byte
LSB Byte
12-Bit Content
Position MSBs
Position LSBs
Measure
8-Bit Content
Position Data
Trailing Zeros
Measure
1
0
Event
Event
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