lm9831 National Semiconductor Corporation, lm9831 Datasheet - Page 34

• Manufacturer Part Number: lm9831
• Description: 42-bit Color, 1200dpi Usb Image Scanner
• Manufacturer: National Semiconductor Corporation

10.4 Suspend Mode: Entering
Suspend Mode is entered when the USB bus has had no activity
for 3ms. The Suspend state forces the LM9831 into a low current
idle state. Suspend Mode:
• Stops the oscillator.
• Forces all black-box highlighted configuration registers to their
• MISC I/O 1-3 will be configured as inputs and can be used as
10.5 Suspend Mode: Exiting
When the LM9831 exits Suspend Mode:
• The oscillator is restarted.
• The Reset and Standby bits are still set. The driver software is
11.0 USEFUL EQUATIONS
The integration time (t
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 LM9831 to generate data any faster then 1Mpixel/s, the
LM9831 will not function correctly. To ensure that the LM9831 is
programmed to a legal datarate, ensure that this constraint is
met:
default settings (including the Reset and Standby bits). See
the Reset and Standby mode descriptions for more
information.
remote wakeup signals.
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.
line_length
t
mclk_divider HDPI_divider
INT
pixel_period
INT
t
=
LINE
) for 1 line is always:
pixel_period line_length
=
=
line_end
=
1+ ITA t
mclk_div C 8
--------------------------------------- -
48MHz
+
INT
TR_time
6
34
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 QUESTIONS AND ANSWERS
Q Where is calibration done?
A Calibration is done on the host computer.
Q Does the LM9831 support 800dpi sensors? 400dpi? XXXdpi?
A Yes. The LM9831 will support any sensor up to a maximum of
13.0 GENERAL NOTES AND TROUBLESHOOTING TIPS
(mclk_divider)(HDPI_divider)(ITA) must be greater than or equal
to 6. If this condition is not met, the LM9831 will not work.
Make sure the gamma tables are programmed with a valid
gamma curve.
Make sure the multiplier gain coefficients are loaded and correct.
(Remember, a gain coefficient of 0 means a GAIN of x0, not x1. If
the gain coefficient = 0 the output code will always be 0.)
Remember that when the LM9831 is reset (reg08 = 0x20) or in
suspend for longer than a few milliseconds (consult your DRAM
datasheet), DRAM refresh will stop and the Gamma and Coeffi-
cient data may be corrupted.
Some of the CCD signals (RS, CP1, and CP2) can have a small
pulse when line_end occurs. Line_end resets these signals and
depending on how they are programmed to go on and off,
line_end can chop off the signal before its programmed off time.
This is not a problem because the truncation occurs at the end of
every line, after all the image data for that line has been digitized.
Registers 4 and 5 only autowrap to 0 from their highest possible
legal address. If an address higher than the highest legal address
is written, it will continue to increment from the illegal address, not
wrap to 0, and unknown operation may occur. This can not hap-
pen unless the host writes an illegal address to the dataport.
The absolute distance between reference sample and signal
sample must be 2 MCLKs or greater, whether CDS is on or off.
16383 pixels x 3 colors. Available horizontal resolutions are
calculated by the optical resolution of the scanner divided by
the HDPI_divider.
scan_stepsize
scan_stepsize
mclk_divider HDPI_divider ITA
=
=
line_length vert_res
------------------------------------------------------- -
line_length vertical_resolution
---------------------------------------------------------------------------------- -
FSPI 4
FSPI 4
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----------------------- -
ITA
6
ITA
+
1