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inputs or outputs.

The state of each pin, True or False (1 or 0), is reflected in the

Status Register.

These are the configurable aspects of these I/O pins:

• Input or Output function. If this bit is set to a 0, the pin is config-

ured as an input. If this bit is set to a 1 the pin is configured as

an output.

• The polarity of the input. If this bit is set to a 1 (Active High), a

high level on that input pin will produce a True reading (1) in the

Status Register. If this bit is set to a 0 (Active Low), a low level

on that input pin will produce a True reading (1) in the Status

• Level or Edge Sensitive. If this bit is set to 0 (Level Sensitive),

the Status Register will reflect the current state at that sensor

input pin. If this bit is set to 1 (Edge Sensitive), the Status Reg-

ister for that input will be True (1) if there were any False to

True transitions at that sensor input pin since the last time the

Status Register was read. Reading the status register clears

the state of all the edge sensitive inputs to False (0).

• PAPER SENSE 1 can be programmed to stop a scan, high

speed forward, or high speed reverse command (by clearing

the Scanning bit) when its state (as reflected in the Status Reg-

ister) changes from False to True. For flatbed scanners this

sensor can be used to detect the home position. In sheetfed

systems, PAPER SENSE 1 can be used to detect whether or

not the user has inserted a document to be scanned.

• PAPER SENSE 2 can be programmed to stop the scan or high

speed forward (by clearing the Scanning bit), and also set its bit

in the Status Register to True a programmable number of lines

after its input pin changes state from False to True. In sheetfed

scanners this is useful if the PAPER SENSE is located before

the scanner array, where the sensor will change states before

all of the paper has been scanned. This can be used in flatbeds

to prevent the motor from trying to step past the limits of travel

of the system. This input should not be used as the home posi-

tion sensor in flatbed scanners, since it will not stop a high

speed reverse command.

• If they are configured as outputs, the MISC I/O 1-6 pins can

have their outputs set to +5V or 0V by writing a 1 or a 0 to the

appropriate bit.

The default state of the MISC I/O pins is described in detail in the

states on power-on, after entering USB Suspend, or when the

RESET pin is pulsed high. A Soft Reset (register 07) does not

reset the MISC I/O pins. The default states of the MISC I/O pins

are:

• MISC I/O 1: Input, edge sensitive, high-to-low transition sets bit

2 of register 2.

• MISC I/O 2: Input, edge sensitive, high-to-low transition sets bit

3 of register 2.

• MISC I/O 3: Input, edge sensitive, high-to-low transition sets bit

4 of register 2.

• MISC I/O 4: Output, voltage on MISC I/O 4 pin = VD.

• MISC I/O 5: Output, voltage on MISC I/O 5 pin = VD.

• MISC I/O 6: Output, voltage on MISC I/O 6 pin = 0V.

5.5.1 Adding Function Buttons

Many scanners today feature multiple buttons to select scan,

copy, fax, email, etc. functions. The LM9833’s MISC I/O pins can

be used for these functions. To free up MISC I/O inputs for other

functions, or if more than 6 buttons are required, you can multi-

plex the buttons together. Figure 36 shows how 7 buttons can be

multiplexed into only 3 MISC I/O lines. Figure 37 shows how to

decode the data in register 2 to determine which button was

pressed. This multiplexing technique can easily be scaled to

allow for more or less buttons with the minimum number of MISC

I/O lines.

5.6 The Brains

This is the master control section that keeps track of the position

of the CCD pixel going through the analog front end, the color of

that line of CCDs (for single output CCD illumination control), the

stepper motor, and all other system coordination.

6.0 Communicating with the LM9833

Everything on the LM9833 (configuration settings, image data,

coefficient data, and gamma tables) is accessed through the

Configuration Register. Configuration Register I/O is done

through two steps. The first step is to write the address (0 through

7F) of the configuration register to be read from or written to. The

second access is the data operation (a read or a write) for that

address. The address only needs to be written once. After an

address is written, any number of reads and/or writes may be

made to that address.

Registers 0, 1, and 2 are read-only registers. Writing to these

addresses may affect various counters inside the LM9833 and

Switch

MISC I/O 1

MISC I/O 2

MISC I/O 3

No Switch

Pressed

Figure 37: Truth Table for Remote Wakeup With Up To

7 Switches

Figure 36: Remote Wakeup With Up To 7 Switches

MISC I/O 1

MISC I/O 2

MISC I/O 3

+5V

22k

22k 22k

Applications Information (Continued)

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