TSC2005 datasheet(32/46 Pages) TI2

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THEORY OF OPERATION

TOUCH SCREEN MEASUREMENTS

Conversion Controlled by TSC2005 Initiated by TSC2005 (TSMode 1)

COORDINATE

OH1

OSC

)2 @ tPVS)tPRE)tSNS)

DLY1

OSC

)2 @ N @ (B)2) @

OSC

ADC

)OHCONV @

OSC

)

PPRO

OSC

(5)

TSC2005

SBAS379C – DECEMBER 2006 – REVISED MARCH 2008

As noted previously in the discussion of the A/D converter, several operating modes can be used that allow great

flexibility for the host processor. This section examines these different modes.

In TSMode 1, before a pen touch can be detected, the TSC2005 must be programmed with PSM = 1 and one of

two scan modes:

1. X-Y-Z Scan (converter function select bits C[3:0] = Control Byte 1 D[6:3] = 0000); or

2. X-Y Scan (converter function select bits C[3:0] = Control Byte 1 D[6:3] = 0001).

See Table 7 for more information on the converter function select bits.

When the touch panel is touched, and the internal pen-touch signal to activates, the PINTDAV output is lowered

if it is programmed as PENIRQ. The TSC2005 then executes the preprogrammed scan function without a host

intervention.

At the same time, the TSC2005 starts up its internal clock. It then turns on the Y-drivers, and after a programmed

panel voltage stabilization time, powers up the A/D converter and converts the Y coordinate. If preprocessing is

selected, several conversions may take place. When data preprocessing is complete, the Y coordinate result is

stored in a temporary register.

If the screen is still touched at this time, the X-drivers are enabled, and the process repeats, but measures the X

coordinate instead, and stores the result in a temporary register.

If only X and Y coordinates are to be measured, then the conversion process is complete. A set of X and Y

coordinates are stored in the X and Y registers. Figure 32 shows a flowchart for this process. The time it takes to

go through this process depends upon the selected resolution, internal conversion clock rate, panel voltage

stabilization time, precharge and sense times, and whether preprocessing is selected. The time needed to get a

complete X and Y coordinate (sample set) reading can be calculated by:

Where:

tCOORDINATE = time to complete X/Y coordinate reading.

tPVS = panel voltage stabilization time, as given in Table 16.

tPRE = precharge time, as given in Table 17.

tSNS = sense time, as given in Table 18.

N = number of measurements for MAV filter input, as given in Table 3 as N.

(For no MAV: M1-0[1:0] = '00', W1-0[1:0] = '00', N = 1.)

B = number of bits of resolution.

fOSC = TSC onboard OSC clock frequency. See Electrical Characteristics for supply frequency (SNSVDD).

fADC = A/D converter clock frequency, as given in Table 15.

OH1 = overhead time #1 = 2.5 internal clock cycles.

OHDLY1 = total overhead time for tPVS, tPRE, and tSNS = 10 internal clock cycles.

OHCONV = total overhead time for A/D conversion = 3 internal clock cycles.

LPPRO = pre-processor preocessing time as given in Table 31.

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