LM9830VJD/NOPB National Semiconductor, LM9830VJD/NOPB Datasheet - Page 25

• Manufacturer Part Number: LM9830VJD/NOPB
• Description: IC SCANNER COLOR DOC 100-TQFP
• Manufacturer: National Semiconductor

Specifications of LM9830VJD/NOPB

• Number Of Bits: 12
• Number Of Channels: 3
• Power (watts): 350mW
• Voltage - Supply, Analog: 5V
• Voltage - Supply, Digital: 4.5 V ~ 5.5 V
• Package / Case: 100-TQFP, 100-VQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *LM9830VJD; *LM9830VJD/NOPB; LM9830VJD

the least significant bit) of the original 8 bit pixel data, and p
cates the original pixel sequence, i.e p
If there are not enough unpacked pixels at the end of a line to
complete the packed byte for transmission, that final byte is not
sent.
The gamma table in 2.5 Gamma Correction Tables allows the
user to set the threshold of each transition for various line art or
reduced pixel depth modes.
2.7 Line Buffer
The line buffer uses the external SRAM to store the pixel data at
the fixed rate and send it back to the PC at an asynchronous,
unpredictable, and non-constant rate.
This buffer is tightly coupled to the stepper motor (3.0 Stepper
Motor Controller), and is responsible for stopping the motor
before the buffer overflows and starting the motor again as the
buffer nears empty.
If the scanner is generating pixel data faster than the PC can
acquire it, the line buffer will start to fill up. As the buffer nears
100% full, the scan must be paused before it starts acquiring a
line it cannot store because of lack of RAM. This Pause Thresh-
old limit (register 4E) is programmable in 1 kbyte increments
between 0 and 255 kbytes but should be no higher than 100% of
the buffer RAM size minus 1 line of data (for single output CCDs
and CIS) or 3 lines of data (for triple output CCDs and CIS).
When this point is reached the buffer sends a command to the
stepper motor controller to stop scanning. The remainder of the
line being processed will continue being processed and be sent
to the buffer. If the Lines To Process After Pause Scan Signal reg-
ister (register 54) is greater than 0, then room for these additional
lines need to be added into the Pause Threshold value calcula-
tion.
After a pause, the buffer will now transmit data to the PC until it
hits the Resume Threshold limit (register 4F), which is also pro-
grammable in 1 kbyte increments between 0 and 256kbytes.
When the Resume Threshold is reached, the Line Buffer sends
the motor controller a command to resume.
Note that the scanner software on the host PC is responsible for
ensuring that the Pause Threshold value is low enough to ensure
that any data that comes after a pause request (the rest of the
current line and any subsequent lines if register 54 bits 0-2 are
greater than 0) will fit into the SRAM buffer size, which is equal to
SRAM size - COEFFICIENT size.
The pause condition is reached when the number of bytes in the
buffer is equal to the value in register 4E * 1024. The scan will
resume when the number of bytes in the buffer is equal to (the
value in register 4F * 1024 + 1023).
Since the external SRAM also contains the pixel gain and offset
data (see 2.2 Pixel Rate Offset Correction Block and 2.3 Pixel
Rate Gain Correction Block), the buffer is as large as the SRAM
size minus the coefficient storage. Supported SRAM sizes are
64kbyte, 128kbyte, and 256kbyte. Coefficient data always takes
up a total of 16kbytes for 300dpi sensors and 32kbytes for 600dpi
sensors.
3.0 Stepper Motor Controller
The stepper motor controller sends a series of pulses to the step-
per motor to move the paper past the sensor (sheetfed) or the
sensor past the paper (flatbed). The speed at which the paper
moves relative to the sensor, combined with the integration time
0
, p
1
, p
2
, p
3
...
n
indi-
25
of the image sensor, determines the effective vertical resolution
(Lines Per Inch, or LPI).
The stepper motor is moved forwards and backwards by two sig-
nals, A and B, 90° out of phase with each other. The phase for the
forward direction is set in Configuration Register 45.
The A and B signals are either squarewaves (in Full Step Mode,
Figure 16), or a staircase approximation of a sine wave (in
Microstep mode, Figures 18 and 19).
The LM9830 always counts stepper motor steps in units of
microsteps. A full step is equal to four microsteps. Even when the
LM9830 is in Full Step Mode, it is counting in microsteps, and will
increment the stepper motor (generating a full step) every four
microsteps.
The microstep Step Size is defined in units of time. These units of
time are pixel periods, as defined in the horizontal pixel counter.
In the 3 channel pixel rate input mode, the pixel period is the
f
modes, the pixel period is equal to f
Size is stored in the Scanning Step Size configuration register
as a 14 bit value. During normal operation, the stepper motor is
advanced 1 microstep every Step Size pixel periods. The LPI can
be calculated as follows:
Where C = the number of full steps required to move the image
one inch, pixels/line is the number of pixel periods it takes to scan
one horizontal line (equivalent to the value stored in the Line End
registers), and StepSize is the number of pixel periods/microstep
Whenever the stepper motor has been moving and then comes to
a stop, the LM9830 waits for the time specified in the Hold Cur-
rent Timeout register and then de-asserts the A, B, A, and B out-
puts to cut power to the motor. When the stepper motor is not
scanning or fast-feeding (Command = 00), A, B, A, and B are de-
asserted in all stepper modes.
There are two modes of stepper motor operation: fullstepping and
microstepping.
3.1 Full Step Mode
In Full Step Mode the output is a pulse stream, as shown in Fig-
ure 16. The amplitude of the pulses is controlled by the output of
ADC
/3 (= f
Figure 16: Stepper Motor Waveform - Full Stepping
A
A
B
B
MCLK
/24). In the 3 channel line rate and 1 channel
LPI
=
4C
1 full step = 4
microsteps
------------------------- -
pixels/line
StepSize
ADC
/3 (= f
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MCLK
/24). The Step