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• Paused until a Resume Scan signal is received. During the hold

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.

• Wait for Resume Scan signal

• Wait for correct number of pixel periods to resynchronize step-

per motor with sensor timing.

• 25% speed forward for y steps (1 step = 4*#pixels in Scanning

Step Size register)

• 50% speed forward for z steps (1 step = 2* #pixels in Scanning

Step Size register).

• Full speed forward (1 step = #pixels in Scanning Step Size

image that they would have been had scanner not stopped.

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

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

are four illumination modes in the LM9830:

In Illumination Mode 1, the lamp connected to the LAMPR pin is

controlled by the LAMPR On/Off settings in the configuration reg-

ister. The LAMPB output (if used) is controlled the same way. If

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 LAMPG output is a Pulse-

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.

In Illumination Mode 2 (which is typically used in conjunction with

1 Channel Mode B), the LAMPR, LAMPG, and LAMPB outputs

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

Illumination

Mode

Description

LAMPR, LAMPG, LAMPB outputs = 0.

This is the power-on default.

Scanning with white light:

LAMPR and LAMPB controlled by

LAMP On/Off pointers in horizontal

pixel counter (as in Mode 3),

LAMPG is a PWM pulse stream

Scanning with 3 LEDs in color:

LAMPR turns on for Red lines

LAMPG turns on for Green lines

LAMPB turns on for Blue lines

Scanning with 3 LEDs in gray:

LAMPR turns on for all lines

LAMPG turns on for all lines

LAMPB turns on for all lines

Figure 27: Illumination Modes

Figure 28: Illumination Mode 1

LAMPG

LAMPR (LAMPR On < Line End, LAMPR Off > Line End)

LAMPB (LAMPB On > Line End, LAMPB Off < Line End)

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