Start Conversion/Write Cycle

TSC2003-Q1

SBAS454 – DECEMBER 2008 ........................................................................................................................................................................................... www.ti.com

Table 1. Possible Input Configurations

REFERENCE

C3

C2

C1

C0

FUNCTION

INPUT TO ADC

X DRIVERS

Y DRIVERS

MODE

0

0

0

0

Measure TEMP0

TEMP0

Off

Off

Single ended

0

0

0

1

Measure VBAT1

VBAT1

Off

Off

Single ended

0

0

1

0

Measure IN1

IN1

Off

Off

Single ended

0

0

1

1

Reserved

—

—

—

Single ended

0

1

0

0

Measure TEMP1

TEMP1

Off

Off

Single ended

0

1

0

1

Measure VBAT2

VBAT2

Off

Off

Single ended

0

1

1

0

Measure IN2

IN2

Off

Off

Single ended

0

1

1

1

Reserved

—

—

—

Single ended

1

0

0

0

Activate X– Drivers

—

On

Off

Differential

1

0

0

1

Activate Y– Drivers

—

Off

On

Differential

1

0

1

0

Activate Y+, X– Drivers

—

X– On

Y+ On

Differential

1

0

1

1

Reserved

—

—

—

Differential

1

1

0

0

Measure X Position

Y+

On

Off

Differential

1

1

0

1

Measure Y Position

X+

Off

On

Differential

1

1

1

0

Measure Z1 Position

X+

X– On

Y+ On

Differential

1

1

1

1

Measure Z2 Position

Y–

X– On

Y+ On

Differential

Table 2. Power-Down Bit Functions

PD1

PD0

PENIRQ

DESCRIPTION

0

0

Enabled

Power-down between conversions

0

1

Disabled

Internal reference off, ADC on

1

0

Enabled

Internal reference on, ADC off

1

1

Disabled

Internal reference on, ADC on

The internal reference voltage can be turned on or off independently of the ADC. This can allow extra time for

the internal reference voltage to settle to its final value prior to making a conversion. Allow this extra wakeup time

if the internal reference was powered down. Also note that the status of the internal reference power down is

latched into the part (internally) when a Stop or repeated Start occurs at the end of a command byte (see

Figure 14 and Figure 16). Therefore, to turn off the internal reference, an additional write to the TSC2003 with

PD1 = 0, is required after the channel has been converted.

It is recommended to set PD0 = 0 in each command byte to get the lowest power consumption possible. If

multiple X-, Y-, and Z-position measurements are done one right after another, such as when averaging, PD0 = 1

leaves the touch screen drivers on at the end of each conversion cycle.

• M: Mode bit. If M is 0, the TSC2003 is in 12-bit mode. If M is 1, 8-bit mode is selected.

• X: Don’t care

When the TSC2003 powers up, the power-down mode bits need to be written to ensure that the part is placed

into the desired mode to achieve lowest power. Therefore, immediately after power-up, a command byte should

be sent which sets PD1 = PD0 = 0, so that the device is in the lowest power mode, powering down between

conversions.

A conversion/write cycle begins when the master issues the address byte containing the slave address of the

TSC2003, with the eighth bit equal to a 0 (R/W = 0), as shown in Figure 12. Once the eighth bit has been

received, and the address matches the A1–A0 address input pin setting, the TSC2003 issues an acknowledge.

Once the master receives the acknowledge bit from the TSC2003, the master writes the command byte to the

slave (see Figure 13). After the command byte is received by the slave, the slave issues another acknowledge

bit. The master then ends the write cycle by issuing a repeated Start or a Stop condition, as shown in Figure 14.

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