BU21026MUV Datasheet, PDF (12/23 Pages) Rohm – 4-wire Resistive Touch Screen Controller

BU21026MUV
Read Protocol
A data read is started in BU21026MUV when the master sends the start condition, the slave address of BU21026MUV, and
one in bit 0( 8^th bit) for reading, as shown in Table 1. If the slave address is matched with its own, BU21026MUV issues an
acknowledge to the master. Next, BU21026MUV send upper 8-bit (D11-4) of an A/D converted 12-bit data as data byte 1
and wait an acknowledge from the master. After receiving the acknowledge, the data byte 2 is sent. Upper 4 bits of it are
lower 4 bits (D3-0) of the A/D converted 12-bit data, and lower 4 bits of it are all zero. In next acknowledge timing, the
master send a not-acknowledge and the stop or repeated start condition for ending read. In the last acknowledge timing,
BU21026MUV doesn’t check the acknowledge and stop sending data. So if the master send an acknowledge and continue
reading a byte, the read data become 0xFF. In the 8-bit mode, all of an A/D converted 8-bit data is in the data byte 1. So,
the master doesn’t need to read the data byte 2.
START
SCL
STOP or
Repeated START
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
Address Byte
Data Byte 1
Data Byte 2
SDA
1
0
0
1
0 AD1 AD0 1
0 D11 D10 D9 D8 D7 D6 D5 D4 0 D3 D2 D1 D0 0
0
0
0
1
SLAVE ADDR
R/WB ^ACK
FROM
MASTER
ACK
FROM
MASTER
NACK
FROM
MASTER
Figure 2. Read Protocol
If an A/D conversion is not finished until falling edge SCL after first acknowledge timing with read mode, SCL pin is
stretched by BU21026MUV.In this state, SCL pin is forced to low by BU21026MUV and SDA value is invalid data. This state
is ended when the A/D conversion is finished. After this state end, the master can control the SCL line and read converted
data.
With stretch function, the master can access immediately after sending a conversion command. If performance of an A/D
conversion is needed, the master send the read command after the A/D conversion is finished. Detail of a A/D conversion
time is shown in Table 5.
Conversion
1
2
3
4
5
6
7
8
9
Stretch
STOP or
Repeated START
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
SCL
Address Byte
SCL low force
by
BU21025
Data Byte 1
Data Byte 2
SDA
1
0
0
1
0 AD1 AD0 1
0
X
D11 D10 D9 D8 D7 D6 D5 D4 0 D3 D2 D1 D0 0
0
0
0
1
SLAVE ADDR
R/WB ^ACK
FROM
MASTER
INVALID
DATA
ACK
FROM
MASTER
NACK
FROM
MASTER
Figure 3. Read with Stretch
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TSZ22111 • 15 • 001
12/19
TSZ02201-0L5L0FF00890-1-2
4.Aug.2016 Rev.001