LM9830VJDX NSC [National Semiconductor], LM9830VJDX Datasheet - Page 28

• Manufacturer Part Number: LM9830VJDX
• Description: LM9830 36-Bit Color Document Scanner
• Manufacturer: NSC [National Semiconductor]

• Paused until a Resume Scan signal is received. During the hold
• Wait for Resume Scan signal
• Wait for correct number of pixel periods to resynchronize step-
• 25% speed forward for y steps (1 step = 4*#pixels in Scanning
• 50% speed forward for z steps (1 step = 2* #pixels in Scanning
• Full speed forward (1 step = #pixels in Scanning Step Size
The Lines to Process After Pause Scan Signal/Lines to Dis-
card After Resume Scan Signal register is not used in reversing
mode.
3.5 Fast Feed Step Size Register
When the motor is being moved quickly (Paper Feed to
End/Paper Feed to Beginning command or Steps to Skip at
Start of Scan register), the microstep period comes from this
register.
For all other motor movement, the step size is given in the Scan-
ning Step Size register.
3.6 Stepper Motor Current Control Using PWM
There is an option to use Pulse Width Modulation of the current in
the stepper motor to increase high speed torque, optimize effi-
ciency, and allow use of a lower current, less expensive motor.
Precisely controlling the current in the motor provides several
benefits. In Full Step Mode, the motor can start moving faster and
overcome inertia by increasing the current to the motor to 100%
when it is starting from a dead stop. After a programmable num-
ber of steps, the inertia is overcome and the current can be
reduced to 66% to reduce heat in the stepper motor (allowing a
less expensive motor to be used). When stopping the stepper
motor, the current is increased to 100% for a short time to over-
come the forward momentum, then the motor is held in position
with a low-level standby current of 30-40%. If the motor is motion-
less for more than the Hold Current Timeout period, the current
goes to 0%.
In microstepping mode, the PWM is used to approximate a sine
wave as shown in Figure 18.
The current control is accomplished by measuring the average
motor winding current through a sense resistor to ground, com-
paring it to a reference voltage, and PWMing the motor driver
transistor to force the current to be equal to the reference current.
See the Stepper Motor Current Controller Block Diagram at
the end of this document.
4.0 Scanner Support Functions
4.1 Illumination Control Block
Scanner systems require an illumination source to supply the
light to the image being scanned. This source may be white (typi-
cally a fluorescent lamp), or red, green, and/or blue LEDs. There
current timeout period, the DAC output is held at 0.125V (the
hold current) for FullStep mode, or the DAC outputs are held as
they were prior to stopping for the microstep mode. After the
hold current timeout period, output drivers A, B, A, and B are
deasserted.
per motor with sensor timing.
Step Size register)
Step Size register).
register), with TR pulses synchronized to same the position on
image that they would have been had scanner not stopped.
28
are four illumination modes in the LM9830:
In Illumination Mode 1, the lamp connected to the LAMP
controlled by the LAMP
ister. The LAMP
the lamp is supposed to be on all the time, then the On setting
should be set to a number between 0 and the value in the Line
End register, and the Off register should be set to a number
greater than the value in the Line End register. Conversely, if the
lamp is supposed to be off all the time, then the On setting should
be set to a number greater than the value in the Line End register,
and the Off register should be set to a number between 0 and the
value in the Line End register. The LAMP
Width-Modulated pulse stream whose duty cycle is controlled by
the value in the PWM register (0-4095). The duty cycle is there-
fore equal to the register value/4096. The PWM counter is
clocked with the CRYSTAL IN frequency so the output frequency
is CRYSTAL IN/4096 (12.2kHz with a 50MHz clock). This PWM
output can be used to control the brightness of a fluorescent
lamp.
LAMP
LAMP
In Illumination Mode 2 (which is typically used in conjunction with
1 Channel Mode B), the LAMP
are cycled through sequentially, one line at a time. An internal
color counter keeps track of the color of the line to be integrated,
and takes that color’s LAMP output high when the pixel counter
reaches the value stored in that color’s LAMP On register (Con-
figuration Registers 2C-37). If the On value is greater than the
value in the Line End register, then that lamp never turns on. That
color’s LAMP output goes low when the pixel counter reaches
that color’s Off value. If the Off value is greater than the value in
the Line End register, then the pixel counter will never reach the
Off value and the lamp will always stay on. Illumination Mode 2
LAMP
TR
0
1
2
3
Illumination
R
B
G
(LAMP
(LAMP
Mode
B
R
Figure 28: Illumination Mode 1
B
On > Line End, LAMP
On < Line End, LAMP
Figure 27: Illumination Modes
output (if used) is controlled the same way. If
LAMP
This is the power-on default.
Scanning with white light:
LAMP
LAMP On/Off pointers in horizontal
pixel counter (as in Mode 3),
LAMP
Scanning with 3 LEDs in color:
LAMP
LAMP
LAMP
Scanning with 3 LEDs in gray:
LAMP
LAMP
LAMP
R
On/Off settings in the configuration reg-
R
R
G
R
G
B
R
G
B
, LAMP
turns on for Blue lines
turns on for all lines
and LAMP
is a PWM pulse stream
turns on for Red lines
turns on for Green lines
turns on for all lines
turns on for all lines
R
, LAMP
Description
G
B
R
, LAMP
Off < Line End)
Off > Line End)
B
G
http://www.national.com
, and LAMP
controlled by
G
B
output is a Pulse-
outputs = 0.
B
R
outputs
pin is