MPR121_10 FREESCALE [Freescale Semiconductor, Inc], MPR121_10 Datasheet - Page 49

• Manufacturer Part Number: MPR121_10
• Description: Proximity Capactive touch Senosr controller
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

Sensors
Freescale Semiconductor
MESSAGE FORMAT FOR WRITING THE MPR121
A write to the MPR121 comprises the transmission of the MPR121’s keyscan slave address with the R/W bit set to 0, followed
by at least one byte of information. The first byte of information is the command byte. The command byte determines which
register of the MPR121 is to be written by the next byte, if received. If a STOP condition is detected after the command byte is
received, the MPR121 takes no further action
command byte are data bytes.
Any bytes received after the command byte are data bytes. The first data byte goes into the internal register of the MPR121
selected by the command byte
If multiple data bytes are transmitted before a STOP condition is detected, these bytes are generally stored in subsequent
MPR121 internal registers because the command byte address generally auto-increments.
MESSAGE FORMAT FOR READING THE MPR121
MPR121 is read using MPR121's internally stored register address as address pointer, the same way the stored register address
is used as address pointer for a write. The pointer generally auto-increments after each data byte is read using the same rules
as for a write. Thus, a read is initiated by first configuring MPR121's register address by performing a write
by a repeated start. The master can now read 'n' consecutive bytes from MPR121, with first data byte being read from the register
addressed by the initialized register address.
OPERATION WITH MULTIPLE MASTER
The application should use repeated starts to address the MPR121 to avoid bus confusion between I
once a master issues a start/repeated start condition, that master owns the bus until a stop condition occurs. If a master that does
not own the bus attempts to take control of that bus, then improper addressing may occur. An address may always be rewritten
to fix this problem. Follow I
Command byte is stored on receipt ofSTOP condition
S
S
S
SLAVE ADDRESS
Command byte is stored on receipt ofSTOP condition
Acknowledge from MPR121
SLAVE ADDRESS
How command byte and data byte
Acknowledge from MPR121
map into MPR121's registers
SLAVE ADDRESS
R/W
2
C protocol for multiple master configurations.
0
R/W
Acknowledge from MPR121
(Figure
A
D15 D14 D13 D12 D11 D10 D9
Figure 54. Command and Single Data Byte Received
0
54).
COMMAND BYTE
A
Acknowledge from MPR121
Figure 53. Command Byte Received
D15 D14 D13 D12 D11 D10 D9
(Figure
R/W
Figure 55. Reading MPR121
0
53) beyond storing the command byte. Any bytes received after the
COMMAND BYTE
D8
A
A
S
Acknowledge from
D15
Repeated Start
MPR121
D14
SLAVE ADDRESS
Acknowledge from MPR121
D8
D13
COMMAND BYTE
A
D12
R/W
D7
Acknowledge from MPR121
1
D6
D11
A
D5
D7 D6
D10
DATA BYTE
D4
1 byte
D5 D4
2
D3
D9
Acknowledge from master
DATA BYTE
C masters.On a I
Acknowledge from
n bytes
D2
D3 D2
(Figure 53)
Auto-increment memory
D8
MPR121
D1
word address
auto-increment memory
D1 D0
word address
A
D0
MPR121
followed
A
A
2
P
C bus,
P
P
Stop
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