LM8400 datasheet(11/20 Pages) NSC

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4.0 Functional Description (Continued)

$B2: Read software version number

Reply Byte #1: $C7 (Software version number)

Byte #2: First byte in version number, year 20 (00-99)

Byte #3: Second byte in version number, month (1-12)

Byte #4: Third byte in version number, day (1-31)

$B3: Read # of calibration points

Reply Byte #1: $CA (Acknowledge)

Byte #2: ($00 — no calibration done, $02 — 2 points,

$05 — 5 points or $0D — 13 points)

$B4: Read stored calibration points

Reply Byte #1: $CA (Acknowledge)

Byte #2: ($00 — no calibration done, $02 — 2 points,

$05 — 5 points or $0D — 13 points)

Byte #3: X-max (2 MSB for coordinate 1)

Byte #4: X-min (8 LSB for coordinate 1)

Byte #5: Y-max (2 MSB for coordinate 1)

Byte #6: Y-min (8 LSB for coordinate 1)

Continue until all coordinates have been sent. A zero is send

back if calibration has not been performed and there are no

data bytes.

$B8: Set focus value

Byte #2: Focus value (0-63)

Reply Byte #1: $CA (Acknowledge)

Byte #2: Focus value (0-63)

The set focus command allows the setting of different values

to improve touch screen focusing. Focusing is defined as the

ability of the touch screen controller to detect exactly identi-

cal coordinate values from measurement to measurement if

the pointer on the touch screen has not moved. The focus

values are equivalent to pixels of touch screen resolution. If

for example a value of 2 is selected, this means that every

coordinate value that is within two pixels of the previously

measured coordinate value is considered to be identical to

that previous value and that in this case the touch screen

controller transmits the previous coordinate information. This

keeps the mouse pointer steady at the point being touched,

rather than "jumping around" the point. A Focus value of zero

disables the focusing algorithm. The default setting is 4.

$BA: Set number of samples per coordinate

Byte #2: Number of samples per coordinate ($01 - 1

samples/coordinate, $02 - 2 samples/coordinate, $04

- 4 samples/coordinate, $08 - 8 samples/coordinate,

$10

samples/coordinate,

$20

samples/coordinate)

Reply Byte #1: $CA (Acknowledge)

Byte #2: Number of samples per coordinate ($01 - 1

samples/coordinate, $02 - 2 samples/coordinate, $04

- 4 samples/coordinate, $08 - 8 samples/coordinate,

$10

samples/coordinate,

$20

samples/coordinate)

This command allows the selection of different sample num-

bers per X, Y, and Z coordinates. The higher the number of

samples per X, Y, and Z coordinates, the better the accuracy,

but the lower the coordinates per second data rate. The

default setting is 8.

$BB: Set communication mode

Byte #2: Communication mode ($01 = stream, $02 =

touchdown, $04 = liftoff)

Reply Byte #1: $CA (Acknowledge)

Byte #2: Communication mode ($01 = stream, $02 =

touchdown, $04 = liftoff)

See the communication modes section for a description of

the stream, touchdown and liftoff modes. This command

selects the communication mode. The default setting is

stream mode.

$BC: Set max delta

Byte #2: Max delta value (0-63)

Reply Byte #1: $CA (Acknowledge)

Byte #2: Max delta value (0-63)

See the averaging algorithms section for a detailed descrip-

tion of this setting. Simply put, this command sets how much

the "coordinate velocity" can change from one coordinate to

the next. The default setting is 8.

$BD: Set calibration points

Byte #2: High nibble: Number of calibration points

($01 = two, $02 = five, $04 = thirteen)

Low nibble: Active calibration cross (1-13 = cross #)

Reply Byte #1: $CA (Acknowledge)

Byte #2: High nibble: Number of calibration points

($01=two, $02=five, $04=thirtheen)

Low nibble: Active calibration cross # (1-13)

Refer to the calibration section for details.

$BE: Set minimum pressure

Byte #2: Minimum pressure value (0-127)

Reply Byte #1: $CA (Acknowledge)

Byte #2: Minimum pressure value (0-127)

This setting controls how high the pressure (Z-axis) must be

in order for samples to be accepted. Setting this value too

low may result in having faulty coordinates accepted. This

value is internally multiplied by two in the controller (due to

the 7-bit limitation in the communication format, which can

not send 8-bit values larger than 127 in one byte). The

default setting is 40.

$A0: Toggle disable/enable external filter path

Reply Byte #1: $CA (Acknowledge)

Byte #2: (0 = now disabled, 1 = now enabled)

This command enable/disable external filter path. The exter-

nal filter path enabled option will require the addition of a

single external low pass filter (either R/C or active OpAmp

based), which is then applied to the touch screen signal

lines. This option can be used in high noise environments to

significantly improve performance and accuracy of the touch

screen controller.

The default setting is filter path enabled.

$A2: Toggle disable/enable self-power down

Reply Byte #1: $CA (Acknowledge)

Byte #2: (0 = now disabled, 1 = now enabled)

This command can switch between self-power down mode

enable or disabled. Refer to the Power Save Mode section

for details. The default setting is Self-Power Down mode

enabled. If the echo mode is enabled, any command byte

send to the device will be echo back and executed.

$A3: Toggle disable/enable echo mode

Reply Byte #1: $CA (Acknowledge)

Byte #2: (0 = now disabled, 1 = now enabled)

The echo mode is available for debugging purposes. If en-

abled, the touch screen controller will echo back any data

that is received via the UART interface.

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