lm9831 National Semiconductor Corporation, lm9831 Datasheet - Page 35

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

The range of values for the Optical Black (registers 0F and 10),
Reset Pulse (11 and 12), CP1 pulse (13 and 14), CP2 pulse (15
and 16), Reference Sample (17), and Signal Sample (18) settings
depend on the rate of the pixel data coming from the sensor.
Always make sure line length (data pixels end - data pixels start)
is >= the horizontal divider. For example, if you are dividing by 12,
the line length must be >=12.
The Line End (registers 20 and 21) setting must be programmed
as follows relative to the Data Pixels End (registers 24 and 25)
setting:
Line End must be >= Data Pixels End + 20
The Data Pixels Start (registers 22 and 23) setting must be >=the
Active Pixels Start (registers 1E and 1F) setting.
The correct Default Phase Difference (registers 52 and 53) must
be set for a scan to restart properly following a pause in the scan-
ning. See the LM9831 software for information on setting the
DPD register.
The number of fullsteps skipped at the start of a scan may be one
less than the Fullsteps to Skip at Start of Scan (registers 4A and
4B) setting.
The Scanning Step Size (registers 46 and 47) and Fast Feed
Step Size (registers 48 and 49) settings must be > 2.
When reverse is enabled, the LM9831 always stops on Red (line
rate color). When reverse is disabled, it will stop on any color.
The contents of register 01 is not reset by the start of a new scan,
but it is updated to the correct value after the first line has been
scanned. To reset this counter prior to starting a scan, the chip
can be briefly reset (register 7 = 0x20). Since resetting the chip
may have undesired consequences (turning the lamp off briefly,
interrupting DRAM refresh), it is also acceptable to simply wait
until register 01 starts incrementing. At that point the register 01
data will be correct.
Gamma and gain/offset coefficient data should be written with
reg07=0 (idle). Do not attempt to write gamma or gain/offset coef-
ficient data when scanning (reg07=03).
14.0 PORTING SOFTWARE FOR LM9830 TO LM9831
The LM9831 is similar in architecture to the LM9830. Porting a
TWAIN driver from the LM9830 to the LM9831 is relatively
straightforward if consideration is given to the following issues.
The LM9831 includes almost all the features of the LM9830, plus
several new ones. The first step is to change the LM9830 Twain
driver so that it works with the LM9831. The second step is to
take advantage of the new features of the LM9831 that will allow
you to obtain even better, faster scans than you obtained with the
LM9830.
14.1 Porting Step 1
14.1.1 Adjust for Register Changes
While more than 50% of the registers in the LM9831 are in the
Pixel Rate Modes
Line Rate Modes
Mode
Pixel Rate
MCLK/24
MCLK/8
Registers 0F to 18
Range
0 - 23
0 - 7
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same location and perform the same function as they did in the
LM9830, many other registers have changed. Sometimes the
address of a register changed, sometimes the location of the bits
inside a register were moved, some register settings were com-
bined or deleted, and the size of some registers was changed.
Please compare the register listings for the LM9830 and LM9831
carefully. This is a list of registers that have changed:
Registers 1, 2, 3, 4, 7, 9, B, 19, 1A, 1B, 3E-41, 42, 43-44, 4E-4F,
51-53, 54, 5A, 5B, 5E.
14.1.2 Choosing the MCLK Divider (Register 0x08)
The datarate coming out of the Horizontal DPI Divider must be
1.1MHz or less. If it is faster than this, the LM9831 will not oper-
ate correctly. Since the maximum USB datarate is about 1MHz,
this does not impact the performance of the scanner in any way.
This is the Clock Divider Rule:
(MCLK_divider)(HDPI_divider)(ITA) >= 6.
The ITA (Integration Time Adjust) refers to register 19, and will be
discussed in a later section. If register 19 = 0, then the value of
ITA = 1 for the purposes of this formula.
If register 19 = 0, this formula means that if the HDPI_divider = 1,
the MCLK_divider must be set to divide-by-6 (reg 08 = 10 [deci-
mal]) or higher. If the HDPI_divider = 4, the MCLK_divider must
be set to divide-by-2 (reg 08 = 2) or higher. If the HDPI_divider is
6 or larger, then the MCLK_divider can be set to divide-by-1
(reg08 = 0).
See 14.2.2 Integration Time Adjustment Function for addi-
tional information.
14.1.3 Calibration
In the LM9830, calibration was always performed at the optical
resolution of the scanner. For example, if the optical resolution of
the scanner was 600dpi, then calibration was performed at
600dpi even if the scan was going to be at 300dpi or 150dpi.
To keep the speed of the LM9831 high while using slower DRAM
(instead of SRAM), the architecture of the LM9831 was changed
so that the Horizontal DPI adjust function is performed before the
pixel rate offset and shading correction, instead of after (as in the
LM9830).
This means that the calibration routine needs to be changed so
that register 9 is set to the desired scan resolution before calibra-
tion.
14.1.4 Pixel Rate Offset Correction
The LM9831 now uses 14 bits for the offset correction of each
pixel. The offset correction data is shifted up to fit into the 16 bit
DRAM. For example, offset correction codes of 3, 31 and 4096
would be transmitted to the dataport as:
0003: 0000 0000 0000 1100
0031: 0000 0000 0111 1100
4096: 0100 0000 0000 0000
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