VD5377 datasheet(49/88 Pages) STMICROELECTRONICS

49 / 88 page

Doc ID 022952 Rev 2

49/88

VD5377

Basic start-up information

8.3

Reading X/Y motion data

The host can service motion data either by polling the motion signal on a regular basis or by

using the motion signal to generate a host interrupt. The procedure for reading X/Y motion

vectors is shown in Figure 20.

Figure 20. Reading X/Y motion

Note:

X/Y motion registers 0x21 and 0x22 must be read consecutively using a multiple location

I2C read sequence. See Section 11.4.4: Multiple location read on page 66.

X/Y motion data is stored internally in a 17-bit accumulator ensuring that no data is lost even

if the host CPU is delayed responding to motion. X/Y motion data is read from the

accumulator using register 0x21 and 0x22 (see Table 29). 0x21/0x22 are 8-bit registers

comprising 7 bits of data plus 1 sign bit. The X/Y_overflow bits (register 0x23 bits 0 and 1)

indicate when the X/Y motion registers are full and there is more than 1 byte of data to be

read. There is no overflow indicator for the accumulator but it is unlikely that an overflow will

ever happen in practice.

Read X/Y Motion

More Motion?

Exit

yes

Motion detected?

(registers 0x21/0x22)

yes

VD5377 数据表(PDF) 49 Page - STMicroelectronics