MAX11800_10 Datasheet, PDF(25/57 Page) Maxim Integrated Products – Low-Power, Ultra-Small Resistive Touch-Screen Controllers with I2C/SPI Interface

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MAX11800_10 Datasheet, PDF (25/57 Pages) Maxim Integrated Products – Low-Power, Ultra-Small Resistive Touch-Screen Controllers with I2C/SPI Interface

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Low-Power, Ultra-Small Resistive Touch-Screen

Controllers with I2C/SPI Interface

The MAX11800âMAX11803 idle in TDM. The TIRQ output

goes low when a touch is detected on the panel indicat-

ing to the AP that a touch is present and a measurement

operation starts.

The AP requests specific panel measurements through

the serial interface. TIRQ stays low during panel setup

and measurement operations. Once a measurement is

complete (with CONT = 0), the MAX11800âMAX11803

check for the continued presence of a touch on the

panel and tag the data accordingly (see Table 6). The

duration of this operation is programmable, specified in

the touch-detect pullup timing configuration register

(0x07). After the data is tagged, the data is available for

readback through the serial interface. The

MAX11800âMAX11803 return to TDM and return control

of TIRQ to the TDM circuitry. TIRQ stays low while a

touch remains present, indicating further measurements

are required, otherwise TIRQ goes high until a new touch

is observed.

Continuous interrupt mode (CINT) allows the complete

control over the measurement operations and direct obser-

vation of the touch status of the panel. Figure 9 shows the

polling of TIRQ when other functions share the TIRQ bus. In

the illustration of Figure 9, no â10â event tag is observed

because the release occurs during a TDM period.

Edge Interrupt Mode

When a touch is present on the panel in edge interrupt

mode, the MAX11800âMAX11803 return to an untimed

high-impedance mode once data tagging operations are

complete. In edge interrupt mode, the duration of a touch

is determined by the tags applied to the measurement

data. Data tagged as initial (00) or midpress (01) indicates

the user needs to continue to scan the panel until a

release is observed. In this state, there is no need to con-

tinue monitoring the touch status prior to the next request-

ed measurement. If a panel touch is not present, data is

tagged as release (10) and the MAX11800âMAX11803

idle in TDM continuously, issuing an interrupt only when

the next panel touch is initiated.

The operation described in the preceding paragraph

makes the edge interrupt mode more efficient than the

continuous interrupt mode. However, the edge interrupt

mode requires continuous scanning of the panel until a

release (10) event is observed. Otherwise, the

MAX11800âMAX11803 do not idle in TDM and are not

able to recognize a change in touch status. New touches

are not recognized and new interrupts are not issued if a

release event is not detected before stopping the conver-

sion sequence.

Table 6. Measurement and Event Tags

(Continuous Interrupt Mode)

MEASUREMENT

MTAG[3:2]

EVENT

Touch (data valid)

N/A (not used)

No touch present (data

invalid)

Measurement in progress

(data invalid)

ETAG[1:0]

PANEL

BEGINNING OF TOUCH EVENT

END OF TOUCH EVENT

TIRQ

TDM

DCM SCAN

ETAG = 00

tAP

tSD

READBACK OPERATIONS ARE NOT SHOWN, BUT ARE EXECUTED DURING TDM PERIODS.

SCAN INTERVAL (tAP) IS CONTROLLED BY THE AP AND THE INITIATION OF DM SCAN EVENTS.

SCAN DURATION (tSD) IS A FUNCTION OF THE SCAN TYPE AND CONFIGURATION SETTINGS.

Figure 9. Continuous Interrupt Mode (Direct Conversion Mode)

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