MAX11800_1010 Datasheet, PDF (23/59 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 stored 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 that
is pending, the entire data stream is read back as
FFFFh and the event tag as 11b, indicating that the cor-
responding measurement is in progress and that the
data stream is to be ignored. For combined 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 function (see the Aperture
Modes and Options section). Each measurement type
uses a single location in the (16-bit) memory. The AP
must retrieve the data from the last requested measure-
ment 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.
LPM only applies when in DCM with edge interrupt
mode or ACM during periods following a conversion
where the panel was observed to be touched and a
subsequent panel measurement is required and/or
scheduled.
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. The device can
be powered down through register 0x0B when no panel
input is expected or needed, and, therefore, no power
is consumed through the panel.
Table 4. Median Averaging Operations
AVERAGING MODE
NUMBER OF
SAMPLES TAKEN
NUMBER OF HIGH
SAMPLES REMOVED
NUMBER OF LOW
SAMPLES REMOVED
NUMBER OF
REMAINING SAMPLES
AVERAGED
1
4
1
1
2
2
8
2
2
4
3
16
4
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
1
0
Byte
MSB Byte
LSB Byte
12-Bit Content
Position MSBs
Position LSBs
Measure
Event
8-Bit Content
Position Data
Trailing Zeros*
Measure
Event
*When using averaging with 8-bit conversions, these positions may be filled with fractional data due to averaging operations.
______________________________________________________________________________________ 23