LM9830 datasheet(33/45 Pages) NSC

33 / 45 page

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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 D5 of register 4 should also be set to a 0 or a 1 to indi-

cate whether the DataPort will be read from (D5 = 1) or written to

(D5 = 0) in subsequent operations. This is required so the

LM9830 can prefetch the data for faster access. The DataPort

Address is automatically incremented after every byte of Gamma

data read/written, or every 2 bytes of Offset/Shading data

read/written (since an Offset/Shading word is 2 bytes wide).

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

series of reads or writes to the DataPort will read from or fill up

that selected memory block at maximum speed.

Registers 4 and 5 should always be (re)written to after register 3

has been changed.

5.1.1 DataPort Type and Color

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

set coefficients, Figure 45) and which color of that memory block

(red, green, or blue, Figure 46) is to be read from or written to.

There is one exception to this: when operating the LM9830 in 1

Channel Mode A, the color is determined by the contents of Reg-

ister 26, bits 3 and 4.

5.1.2 DataPort Address

This 13 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 each

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

the range is 0 to 1023. For the Gain and Offset Coefficients this

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

the Valid Pixels Start register) to 2729 (the maximum number of

image pixels for a 300dpi sensor) or 5460 (the maximum number

of image pixels for a 600dpi sensor). If reads or writes continue

past 1023, 2729, or 5460, the DataPort address counter wraps

back around to 0 and continues counting. Note that for Gain and

Offset Coefficients it takes 2 read/write operations to increment

the address counter, because Gain and Offset Coefficients are

stored as a 2 byte word.

5.1.3 DataPort

This 8 bit register (at Configuration Register address 6) is where

the data is sequentially read from or written to. Gamma data is 8

bits wide. Since offset data may be 6 or 8 bits wide and gain cor-

rection data may be 10 or 8 bits wide, these bytes need to be

combined before they are transmitted. For a 6/10 offset/gain bit

split, the format is shown in Figure 47:

The first byte = Offset * 4 + INT(Gain/256), and

The second byte = Gain AND 255.

An 8/8 offset/gain split is more obvious:

If the offset/gain split is changed from 8/8 to 6/10, or from 6/10 to

8/8, the offset and gain coefficients must be re-calculated and

resent to the LM9830.

In Gamma mode, the DataPort address counter is automatically

incremented after a byte is read from or written to register 6. In

Gain/Offset mode, the DataPort address counter is automatically

incremented after two bytes are read from or written to register 6.

Reading and writing the DataPort should only be done when the

LM9830 is not scanning.

6.0 The Parallel Port Interface

The primary interface of the LM9830 is a PC compatible parallel

port interface. This communication mode is selected by tying the

CMODE pin to DGND. There are two operational parallel port

modes for reading data: Nibble Mode (for compatibility with the

maximum number of existing PCs) and EPP (for maximum speed

on newer machines). In addition, the LM9830 supports a printer

passthrough function that allows an LM9830-based scanner to be

inserted between a PC and a printer.

6.1 The Parallel Port Pins

The parallel port on a standard PC has a total of 17 I/O lines: 8

DataPort

Address

(LSB)

b7 - b0

DataPort

b7 - b0

76543210

Type

-----

Gamma

-----

Offset & Gain

Figure 45: DataPort Target Pointer

76543210

Color

-----

Red

-----

Green

-----

Blue

-----

Undefined

Figure 46: DataPort Color Pointer

Configuration

Address

Name

Bits

Figure 44: DataPort

543210

Type

O5 O4 O3 O2 O1 O0 G9 G8

First Byte

G7 G6 G5 G4 G3 G2 G1 G0

Second Byte

Figure 47: DataPort Target Pointer (6/10 split)

543210

Type

O7 O6 O5 O4 O3 O2 O1 O0

First Byte

G7 G6 G5 G4 G3 G2 G1 G0

Second Byte

Figure 48: DataPort Target Pointer (8/8 split)

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