MAX11800_1010 Datasheet, PDF (34/59 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
FIFO Data Word Structure
Table 11 shows a 16-bit data word (MSB byte + LSB
byte). Each data word consists of 12 bits of position
data, mapped to locations [15:4]. Eight-bit measure-
ment data are left-adjusted and mapped to locations
[15:8] and followed by four trailing zeros if averaging is
off. If averaging is on, the 4 bits contain random data as
a result of the summation and division process. Table
12 shows a 2-bit measurement tag indicating the mea-
surement type (X, Y, Z1, or Z2), appended in locations
[3:2]. Table 13 shows a 2-bit event tag indicating where
the sample occurs within a touch event (initial, mid-
press, or release) in locations [1:0].
All data for a given scan operation is tagged according
to the touch status observed at the end of the scan
block measurement operations. For example, if a
requested X, Y, Z1, Z2 scan block contains a release
event, all the data words are tagged 10 before being
written to the FIFO.
An event tag of 11 indicates that the data readback
operation reaches the end of the current FIFO data log
(end of file marker) and there is no unread data in the
FIFO. Terminate the readback operation to await the
next interrupt. Ignore all data with the 11 event tag.
Clearing Interrupt
The FIFO is only used in the autonomous mode with the
clear-on-read interrupt. The interrupt is cleared only
when the newest data block currently available in the
FIFO is loaded for readback. The interrupt does not
clear if there is any unread data block remaining in the
FIFO once a scan block result is loaded. The FIFO does
not check for partial block readbacks. Once the last
available FIFO data block is loaded for readback, the
interrupt clears regardless of whether the readback
operation for that block is complete.
Aperture Modes and Options
The aperture modes available with the MAX11800/
MAX11801 implement spatial filtering. The MAX11800/
MAX11801 contain the required logic to examine panel
measurement data and determine if the data meets the
aperture requirements to be written to the FIFO. Aperture
testing decreases the number of entries in the FIFO to
the minimum required to implement the intended appli-
cation. The elimination of extraneous FIFO data events
reduces activity on the TIRQ line, serial bus, and mini-
mizes AP overhead. The contents in the FIFO are not
necessarily linearly sampled in time when the device is in
aperture mode.
Block Readback Operations
The MAX11800/MAX11801 do not support partial block
readback operations. Each readback operation loads
an entire scan block result (32, 48, or 64 bits) into a
temporary location for serial readback. A scan block is
marked as read in the FIFO once a scan block result is
loaded, freeing the memory space for the subsequent
measurements. Once initiated, the AP must complete
the full readback cycle for the block requested or the
unread portions of the block data is lost.
Table 11. FIFO Data Word Structure
Aperture Range Requirements
Program the aperture range requirements for both X
and Y through register 0x0B. Range requirements are
expressed as distance, in position LSBs. The blanking
aperture extends from the initial touch position, both
±ΔX and ±ΔY with 12-bit resolution (1 LSB = 1/4096 of
the corresponding screen dimension). An aperture set-
ting of 0x00 effectively disables aperture checking with
all measurement data logged to the FIFO. Apertures
are specified in a power-of-two format: ΔX = 2^APRX[3:0]-1
and ΔY = 2^APRY[3:0]-1.
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.
Table 12. FIFO Data Measurement Tags
Table 13. FIFO Event Tags
MEASUREMENT
X
Y
Z1
Z2
TAG[3:2]
00
01
10
11
EVENT
Initial touch
Midpress
Release (data invalid)
End of file indicator
(FIFO data invalid)
TAG[1:0]
00
01
10
11
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