LM8500HVA9 National Semiconductor, LM8500HVA9 Datasheet - Page 14

• Manufacturer Part Number: LM8500HVA9
• Description: IC TOUCHSCREEN CONTROLLER 44PLCC
• Manufacturer: National Semiconductor
• Type: Resistiver

Specifications of LM8500HVA9

• Touch Panel Interface: 4-Wire
• Number Of Inputs/keys: 1 TSC
• Resolution (bits): 10 b
• Data Interface: UART
• Data Rate/sampling Rate (sps, Bps): 38.4k
• Voltage - Supply: 2.7 V ~ 5.5 V
• Current - Supply: 11.5mA
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 44-PLCC
• Voltage Supply Source: Single Supply
• For Use With: LM8500-REF-01 - BOARD EVALUATION LM8500
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Sampling Rate (per Second): -
• Other names: *LM8500HVA9

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12.0 Averaging Algorithm
12.2 FOCUS ALGORITHM
The focus algorithm removes some inaccuracy and noise
that could cause the coordinate to differ only by a couple of
pixels. The focus algorithm is used to eliminate the "jittering"
effect of the pointer when the pointer is stationary.
The focus algorithm compares the value of the previous
stored value to the value passed from the delta algorithm
and determines if the difference is greater than or equal to
the Set Focus Value. If the difference is greater or equal to
the value in Set Focus Value then the new coordinate is sent
out through the UART and stored as the previous value. If
the difference is less than the Set Focus Value then the
value is discarded and the stored valued is set through the
UART.
The amount of difference between the new coordinate and
the old coordinate is set in the Set Focus Value. This value
can be from 0-63 with a value of 0 disabling the focus
algorithm. The factory default is 4.
12.3 COMMUNICATION MODES
Liftoff
When set to the liftoff mode, the controller only sends data
through the UART on liftoff. The controller continuously
samples the touchscreen as long as there is a touch de-
tected on the touchscreen but only the last coordinate is sent
out to the UART.
Touchdown
When set to the touchdown mode, the controller only sends
data through the UART on touchdown. The controller con-
tinuously samples the touchscreen as long as there is a
touch detected on the touchscreen but only the first coordi-
nate is sent out to the UART.
Streaming
When set to the streaming mode, the controller continuously
sends data through the UART as long as there is a touch
detected on the touchscreen.
13.0 Brownout Reset
The device is initialized when the RESET pin is pulled low or
the On-chip Brownout Reset is activated.
The RESET input initializes the device when pulled low. The
RESET pin must be held low for a minimum of 0.5µs for the
LM8500 and a minimum of 1.5µs for the LM8300 to guaran-
tee a valid reset. Reset should also be wide enough to
ensure crystal start-up upon power-up. The R/C circuit
shown in Figure 3 is an optional circuitry that will provide a
delay 5 times (5x) greater than the power supply.
(Continued)
14
When enabled, the device generates an internal reset as
V
voltage (V
= 120-128 µs for the LM8500 and t
LM8300. Once the t
released and the controller resume normal operation. This
internal reset will perform the same functions as external
reset. Once V
instruction execution begins. If, however, V
the selected V
to 120-128 µs for the LM8500 and 360-384 µs for the
LM8300. The device now waits until V
at which time the countdown starts over. When enabled, the
functional operation of the device, at frequency, is guaran-
teed down to the V
One exception to the above is that the brownout circuit will
insert a delay of approximately 3 ms on power up or any time
the V
be held in Reset for the duration of this delay before t
count down. This delay starts as soon as the V
above the trigger voltage (approximately 1.8V). This behav-
ior is shown in Figure 4.
In Case 1, V
undefined until the supply is greater than approximately
1.0V. At this time the brownout circuit becomes active and
holds the device in RESET. As the supply passes a level of
about 1.8V, a delay of about 3 ms (td) is started and t
preset with 120-128 µs for the LM8500 or 360-384 µs for the
LM8300. Once V
t
Case 2 shows a subsequent dip in the supply voltage which
goes below the approximate 1.8V level. As V
V
back above the 1.8V level, td is started. Since the power
supply rise time is longer for this case, td has expired before
V
greater than V
Case 3 shows a dip in the supply where V
V
V
goes back above V
FIGURE 3. Optional Reset Circuit using External Reset
id
CC
bor
CC
bor
CC
starts to count down.
, the internal RESET signal is asserted. When V
, but not below 1.8V. On-chip RESET is asserted when
rises above V
goes below V
rises. While V
CC
drops below a voltage of about 1.8V. The device will
bor
), the device is held in the reset condition for t
CC
bor
bor
CC
, an internal reset is generated, and t
CC
.
rises from 0V and the on-chip RESET is
is above the V
bor
bor
bor
bor
CC
is greater than V
id
and t
.
level.
and t
is less than the specified brownout
reaches zero, the internal reset is
id
id
starts immediately when V
starts as soon as the supply
bor
id
bor
CC
and t
= 360-384 µs for the
is greater than V
and td has expired,
id
CC
CC
CC
reaches zero,
drops below
drops below
drops below
20037205
CC
CC
id
id
starts
is set
CC
rises
rises
id
bor
is
is
id
,