BU21028FV-M Datasheet, PDF (8/36 Pages) Rohm – 4-wire Resistive Touch Screen Controller

BU21028FV-M
Host Interface Specification
The BU21028FV-M controller operates as an I2C slave device. At the start of the communication, it receives an address
byte transmitted by the host processor and then then sends back an acknowledgement byte. The host processor can
transmit a command to execute conversion or to access registers only after receiving the acknowledgement for the address
byte. Communication ends when BU21028FV-M receives a stop command.
●Address byte
On the address byte, the slave address for 2-wire interface is written on the upper 7 bits and the READ/WRITE bit is written
on the last bit. The upper six bits of the slave address are fixed to “100000” while the last bit is determined by the “AD0”
input.
Table 1. Serial Interface Slave Address Byte
MSB
D7
D6
D5
D4
D3
D2
D1
LSB
D0
1
0
0
0
0
0
A0
R/W
Bit D1: A0
Slave address bit0 (AD0)
Bit D0: R/W
1=read (reading data)
0=write (writing data)
●Command byte
The operation of BU21028FV-M is dictated by the command byte. The host processor sets CID (D7) to 1 for conversion
function or to 0 for register access.
Table 2. Serial Interface Command Byte 1(CID=1)
MSB
D7
D6
D5
D4
D3
D2
1
CF
CMSK
Bit D7: Command Byte ID
1= Command Byte 1(starts the conversion function determined by CF (Bit D6-D3)
D1
PDM
LSB
D0
STP
Bits D6-D4: CF
Conversion function is selected as detailed below.
Table 3. BU21028FV-M Conversion Function List
CF Description
0x0 Touch screen scan function: X, Y, Z1 and Z2 coordinates and converted.
0x1 NOP
0x2 Auxiliary input converted.
0x3 Reserved
0x4 Free scan function: Drivers status and input of A/D assignment by Host.
0x5 Calibration: Parameters which used dual touch detection calibrated.
0x6 NOP
0x7 NOP
0x8 X+, X- drivers status.
0x9 Y+, Y- drivers status.
0xA Y+, X- drivers status.
0xB NOP
0xC Touch screen scan function: X coordinate converted.
0xD Touch screen scan function: Y coordinate converted.
0xE Touch screen scan function: Z1 and Z2 coordinates converted.
0xF Reserved
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27.May.2016 Rev.002