AT42QT2120 Datasheet

16
9634E–AT42–06/12
AT42QT2120
1. The host initiates the transfer by sending the START condition
2. The host follows this by sending the slave address of the device together with the
WRITE bit.
3. The device sends an ACK.
4. The host then sends the memory address within the device it wishes to write to.
5. The device sends an ACK.
6. The host transmits one or more data bytes; each is acknowledged by the device
(unless trying to write to an invalid address). Valid write address are 5 – 51.
7. If the host sends more than one data byte, they are written to consecutive memory
addresses.
8. The device automatically increments the target memory address after writing each data
byte.
9. After writing the last data byte, the host should send the STOP condition.
Note: the host should not try to write to addresses outside the range 0x06 to 0x33 (6 – 51)
because this is the limit of the device’s internal memory address.
4.3.3 Reading Data From the Device
The sequence of events required to read data from the device is shown next.
1. The host initiates the transfer by sending the START condition
2. The host follows this by sending the slave address of the device together with the
WRITE bit.
3. The device sends an ACK.
4. The host then sends the memory address within the device it wishes to read from.
5. The device sends an ACK if the address to be read from is less than 0x63 otherwise it
sends a NACK).
6. The host must then send a STOP and a START condition followed by the slave
address again but this time accompanied by the READ bit.
Note: Alternatively, instead of step 6, a repeated START can be sent so the host does not
need to relinquish control of the bus.
7. The device returns an ACK, followed by a data byte.
8. The host must return either an ACK or NACK.
a. If the host returns an ACK, the device subsequently transmits the data byte from
the next address. Each time a data byte is transmitted, the device automatically
increments the internal address. The device continues to return data bytes until the
host responds with a NACK.
b. If the host returns a NACK, it should then terminate the transfer by issuing the
STOP condition.
9. The device resets the internal address to the location indicated by the memory address
sent to it previously. Therefore, there is no need to send the memory address again
when reading from the same location.
SLA+W
MemAddress
AAS
S
SLA+R A
A
P
Host to Device Device Tx to Host
P
A
A
Data 1
Data 2
Data n