17

Motion

Address: 0x02

Access: Read/Write

Reset Value: 0x00

Bit

7

654

3

2

1

0

Field

MOT

PIXRDY

PIXFIRST

OVF

Reserved

Reserved

Reserved

Reserved

Data Type: Bit field.

USAGE: Register 0x02 allows the user to determine if motion has occurred since the last

time it was read. If the MOT bit is set, then the user should read registers 0x03 and 0x04 to get

the accumulated motion. Read this register before reading the Delta_Y and Delta_X registers.

Writing anything to this register clears the MOT and OVF bits, Delta_Y and Delta_X registers. The

written data byte is not saved.

Internal buffers can accumulate more than eight bits of motion for X or Y. If either one of the

internal buffers overflows, then absolute path data is lost and the OVF bit is set. This bit is

cleared once some motion has been read from the Delta_X and Delta_Y registers, and if the

buffers are not at full scale. Since more data is present in the buffers, the cycle of reading the

Motion, Delta_X and Delta_Y registers should be repeated until the motion bit (MOT) is cleared.

Until MOT is cleared, either the Delta_X or Delta_Y registers will read either positive or negative

full scale. If the motion register has not been read for long time, at 400 cpi it may take up to 16

read cycles to clear the buffers, at 800 cpi, up to 32 cycles. To clear an overflow, write anything

to this register.

The PIXRDY bit will be set whenever a valid pixel data byte is available in the Pixel_Dump

register. Check that this bit is set before reading from Pixel_Dump. To ensure that the

Pixel_Grab pointer has been reset to pixel 0,0 on the initial write to Pixel_Grab, check to see if

PIXFIRST is set to high.

Field Name

Description

MOT

Motion since last report

0 = No motion

1 = Motion occurred, data ready for reading in Delta_X and Delta_Y registers

PIXRDY

Pixel Dump data byte is available in Pixel_Dump register

0 = data not available

1 = data available

PIXFIRST

This bit is set when the Pixel_Grab register is written to or when the complete pixel array has been

read, initiating an increment to pixel 0,0.

0 = Pixel_Grab data not from pixel 0,0

1 = Pixel_Grab data is from pixel 0,0

OVF

Motion overflow,

∆Y and/or ∆X buffer has overflowed since last report

0 = no overflow

1 = Overflow has occurred