LM8300 datasheet(9/20 Pages) NSC

9 / 20 page

4.0 Functional Description (Continued)

WD_Out — Watch dog output. For correct operation, this

pin should be connected to the RESET pin.

OSC_OUT — Clock oscillator output pin.

OSC_IN — Clock oscillator input pin

GND — Digital Ground

AGND — Analog ground

CC — Digital power supply.

CC — Analog power supply. For best performance, this

pin should be connected to a filter.

Users of the LLP package are cautioned to be aware that the

central metal area and the pin 1 index mark on the bottom of

the package may be connected to GND. See figure below:

4.3 USART Framing Format

The device communicates with the touch screen driver using

the UART set at a baud rate of 38400, 8, n, 1.

All communication from the host software and the controller

consists of a command byte and occasionally data byte(s). If

data byte(s) follow a command byte, it must be sent directly

after the command byte. If the device is in the power save

mode, a delay must be inserted between the wake up com-

mand and the command byte. Refer to the Power Save

mode section for more details. For every command byte sent

to the controller, an acknowledge byte is sent back and

sometimes data byte(s).

A command byte is distinguished by having the 7th bit of the

command byte set (1). If any data byte(s) is to follow, the 7th

bit of the data byte is reset (0).

Data packets sent to the host software can be either four or

five bytes in length. If the pressure measurement is enabled,

five bytes are sent. If the pressure measurement is not

enabled, four bytes are sent.

The first byte of each data packet is a header byte. This

header byte is used to synchronize and differentiate between

four or five byte packages. If a four byte data package is

sent, the 4th bit of the header byte is reset (0). If a five byte

data package is sent, the 4th bit of the header byte is set (1).

The 6th bit of the second byte of the data packet is used to

indicate the touch state. If the bit is set (1), then a touchdown

or continuous touch is detected. If the bit is reset (0), then a

liftoff is detected.

4.3.1. Data packet format table

Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

Byte 1

Byte 2

Byte 3

Byte 4

Byte 5

L - Package length. (0 = 4 bytes,1=5 bytes)

S - Touch state (0 = liftoff, 1 = touchdown or continuous

touch)

X - X position (10 bit value)

Y - Y position (10 bit value)

Z - Z positon (7 bit value), this byte is only transmitted if the

pressure measurement is enabled

4.3.2 Command Bytes

Command

Byte 1

Byte 2

TSC

Byte 1

TSC

Byte 2

Read

clock-speed

(3,33MHz,

10MHz)

$B0

$CA

$00, $01

Read

parameters

$B1

$CA

4.3.3

Advanced

Command

Bytes

Descriptions

Read

software

version

number

$B2

$C7

4.3.3

Advanced

Command

Bytes

Descriptions

Read # of

calibration

points

$B3

$CA

$00, $02,

$05, $0D

Read stored

calibration

points

$B4

$CA

4.3.3

Advanced

Command

Bytes

Descriptions

Set focus

value (# of

pixels on

touch panel)

$B8

$0-$3F

$CA

$00-$3F

Set#of

samples per

coordinate (1,

2, 4, 8, 16,

32)

$BA

$01, $02,

$04, $08,

$10, $20

$CA

$01, $02,

$04, $08,

$10, $20

Set

communication

mode

(stream,

touchdown,

liftoff)

$BB

$01, $02,

$04

$CA

$01, $02,

$04

20037216

FIGURE 1. LLP Package Bottom View

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