LM9832 datasheet(31/42 Pages) NSC

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6.1 The DataPort: Reading and Writing to Gamma, Offset,

and Gain Memory

Because the gamma table and the shading and offset correction

blocks of RAM are very large, the LM9832 uses an indexed

method of reading and writing them, called the DataPort. Four

addresses in the Configuration Register are used to implement

this feature, as shown in Figure 38.

The DataPort allows the user to select a memory block (gamma,

gain coefficient, or offset coefficient) and color (red, green, or

blue) to be read from or written to, by writing to Configuration

The starting address of that block (usually 0) is written into the

DataPort Address register (at Configuration Register Addresses

4 and 5). Bit D6 of register 4 should also be set to a 0 or a 1 to

indicate whether the DataPort will be read from (D6 = 1) or written

to (D6 = 0) in subsequent operations. This is required so the

LM9832 can prefetch the data for faster access. The DataPort

Address is automatically incremented after every word (2 bytes)

of Offset, Shading, or Gamma data is read/written.

Once the memory block, color, and starting address are written, a

series of reads or writes to the DataPort will read from or write to

the selected memory block at maximum speed.

Registers 4 and 5 should always be written to after Register 3 has

been changed.

Reading and writing the DataPort should only be done when the

LM9832 is not scanning (Register 07 = 0).

6.1.1 DataPort Type and Color

These 3 bits determine which memory block (gamma, gain, or off-

set coefficients, Figure 39) and which color of that memory block

(red, green, or blue, Figure 40) is to be read from or written to.

6.1.2 DataPort Address

This 14 bit register (at Configuration Register addresses 4 and 5)

determines what the starting address is for the read/write opera-

tion.

This address is automatically incremented after every 2 byte

word read/write operation to the actual DataPort. For the gamma

table the range is 0 to 4093. For the Gain and Offset Coefficients

this range is 0 (corresponding the first valid pixel as programmed

in the Valid Pixels Start register) to 16383 (the maximum number

of image pixels). If reads or writes continue past 4093 or 16383,

the DataPort address counter wraps back around to 0 and contin-

ues counting.

6.1.3 DataPort

The DataPort is the 8 bit register (Configuration Register address

06) where the data is sequentially read from or written to. The for-

mats for Offset, Gain, and Gamma data are shown in Figures 41,

42, and 43.

7.0 The USB Interface

The LM9832 uses the USB (Universal Serial Bus) interface.

Refer to the LM9832 software package for details on USB com-

munication.

7.1 The USB Pins

Data is received and transmitted through the D+ and D- pins.

These are 3V differential signals. Figure 44 shows the recom-

mended circuitry between the LM9832’s D+ and D- pins and the

scanner’s USB connector.

Configuration

Address

Name

Bits

DataPort

Target/

Color

b3- b0

DataPort

Address

(MSB)

b13 - b8

DataPort

Address

(LSB)

b7 - b0

DataPort

b7 - b0

Figure 38: DataPort

7654

3210

Type

------

Offset

------

Gain

------

Gamma

------

Undefined

Figure 39: DataPort Target Pointer

765432

Color

----

Red

----

Green

----

Blue

----

Undefined

Figure 40: DataPort Color Pointer

7654

Type

b13

b12

b11

b10

First Byte

Second Byte

Figure 41: DataPort Offset Format

7654

Type

b15

b14

b13

b12 b11 b10

First Byte

Second Byte

Figure 42: DataPort Gain Format

7654

Type

0000

b11 b10

First Byte

Second Byte

Figure 43: DataPort Gamma Format

Applications Information (Continued)

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