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10.2 Soft Reset

A Soft Reset is generated by setting bit 5 of register 07. A Soft

Reset:

• Stops most of the internal clocks inside the system to save

power.

• Does NOT stop 48MHz oscillator.

• Resets internal state machines for correct operation after

• Stops DRAM refresh. This will corrupt all the gamma, offset,

gain values, as well as any image data, stored in the external

DRAM.

• Does NOT prevent configuration register read/writes.

10.3 Standby

The LM9832 enters the Standby mode by setting bit 4 of register

07. Standby Mode:

• Powers down the analog section to conserve power.

• Tristates the stepper motor outputs (regardless of the state of

• Does NOT prevent configuration register read/writes.

10.4 Suspend Mode: Entering

Suspend Mode is entered when the USB bus has had no activity

for 3ms. The Suspend state forces the LM9832 into a low current

idle state. Suspend Mode:

• Stops the oscillator.

• Forces all black-box highlighted configuration registers to their

default settings (including the Reset and Standby bits). See

the

Reset

and

Standby

mode

descriptions

for

information.

• MISC I/O 1-3 will be configured as inputs and can be used as

remote wakeup signals.

10.5 Suspend Mode: Exiting

When the LM9832 exits Suspend Mode:

• The oscillator is restarted.

• The Reset and Standby bits are still set. The driver software is

responsible for clearing them and setting the configuration

registers again to resume operation. All configuration registers

and DRAM data should be re-written after a Suspend

sequence.

11.0 USEFUL EQUATIONS

The integration time (tINT) for 1 line is always:

where pixel_period is the time it takes to clock one pixel out of the

sensor (C = 3 for Pixel Rate Color, and 1 for all other modes):

and line_length is the length of an entire line, measured in units of

pixels. Note that this includes the transfer portion of the line:

These equations apply for any ITA (Integration Time Adjust, Reg-

ister 19) setting.

To maximize scanner throughput, it is desirable to generate data

at the same rate as the digital I/O to the host PC. Under some

conditions (slow digital I/O, or very high resolution scans), the

time to generate one line may be greater than the maximum inte-

gration time. In this case, the integration time may be set to an

acceptable value using the previous equations, and the time to

process a line extended using Register 19 (the ITA function).

Using the ITA function, the time to process 1 line can be extended

to match the digital I/O rate required:

The maximum DRAM write pixel rate allowed is 1MHz. If you con-

figure the LM9832 to generate data any faster then 1Mpixel/s, the

LM9832 will not function correctly. To ensure that the LM9832 is

programmed to a legal datarate, ensure that this constraint is

met:

When using the ITA function (ITA > 0), use this version of the

equation:

Use this equation to calculate the stepsize for a scan:

where vertical_resolution = the desired vertical resolution of the

scan, and FSPI = the number of full steps required to move the

sensor one inch.

When using the ITA function (ITA > 0), use this version of the

equation to compensate for the ITA function:

12.0 CHANGES FROM THE LM9831

12.1 FullStep Timeout Function

The LM9832 features a motor step counter that will automatically

stop the scan after a certain number of motor steps. To enable

this mode, set register 58, bit 5 = 0, then program the number of

fullsteps to scan.

12.2 14 Bit Output Mode

The LM9832’s 14 bit output mode is fully functional. It is capable

of scanning any image that the LM9832 can scan at 8 bits, and

does not require any polling of register 01.

12.3 Steps to Reverse Register Increased

To improve performance with some mechanical designs, the

number of bits in register 50 was increased from 6 to 8 bits. This

allows the scanner to reverse up to 255 steps when pausing due

to a buffer full condition.

INT

pixel_period line_length

⋅

pixel_period

mclk_div C 8

⋅⋅

48MHz

----------------------------------------

line_length

line_end

TR_time

LINE

1+ ITA

()t

INT

mclk_divider HDPI_divider

≥

⋅

mclk_divider HDPI_divider ITA

≥

⋅⋅

scan_stepsize

line_length

vertical_resolution

⋅

FSPI

⋅

-----------------------------------------------------------------------------------

scan_stepsize

line_length

vert_res

⋅

FSPI

⋅

--------------------------------------------------------

ITA

()

ITA

------------------------

⋅

Applications Information (Continued)

LM9832 Datasheet(PDF) 34 Page - National Semiconductor (TI)

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