PixArt Imaging Inc.
ADBS-A350 Optical Finger Navigation
START Condition
STOP Condition
SCL driven
by host
SDA driven
by host
SDA falls while
SCL is high
SDA rises while
SCL is high
Figure 19. TWI Start and Stop operation
Acknowledge/Not Acknowledge Bit
After a start condition, a single acknowledge/not acknowledge bit follows each Eight-bit data packet. The device
receiving the data drives the acknowledge/not acknowledge signal on SDA. Acknowledge (ACK) is defined as 0 and not
acknowledge (NAK) is defined as 1.
Packet Formats
Read and write operations between the host and the ADBS-A350 use three types of host driven packets and one type of
ADBS-A350 driven packet. All packets are eight bits long with the most significant bit first, followed by an acknowledge
bit.
Slave Device Address (DA)
Command packets contain a 7-bit ADBS-A350 device address and an active low read/write bit (R/W).
First bit of
packet
Last bit of
packet
Device Address
DA[3]
R/W
Write = 0
Read = 1
DA[6]
DA[5]
DA[4]
DA[2]
DA[1]
DA[0]
Register Address Packets (RA)
The address packets contain an auto-increment (ai) bit and a 7-bit address. If the ‘ai’ bit is set, the slave will process data
from successive addresses in successive bytes. For example, registers 0x01, 0x02, and 0x03 can be written by setting
the ‘ai’ bit to one with address 0x01. The host would send three bytes of data, and the host would terminate with a P
condition.
First bit of
packet
Last bit of
packet
Auto
Register Address
RA[3]
increment
Auto
increment=1,
No
RA[6]
RA[5]
RA[4]
RA[2]
RA[1]
RA[0]
increment=0
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20
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