MPR121
Sensors
Freescale Semiconductor, Inc.
11
5
Register Operation Descriptions
5.1
Register Read/Write Operations and Measurement Run/Stop Mode
After power on reset (POR) or soft reset by command, all registers are in reset default initial value (see
Table 2). All the registers,
except registers 0x5C (default 0x10) and 0x5D (default 0x24), are cleared.
Registers 0x2B ~ 0x7F are control and configuration registers which need to be correctly configured before any capacitance
measurement and touch detection.
Registers 0x00 ~ 0x2A are output registers updating periodically by the MPR121 in Run Mode. Among these output registers,
Baseline Value Registers 0x1D ~ 0x2A are also writable, this is sometimes useful when user specific baseline values are desired.
The MPR121’s Run Mode and Stop Mode are controlled by control bits in Electrode Configuration Register (ECR, 0x5E). When
all ELEPROX_EN and ELE_EN bits are zeros, the MPR121 is in Stop Mode. While in Stop Mode, there are no capacitance or
touch detection measurement on any of the 13 channels. When any of the ELEPROX_EN and ELE_EN bits are set to ‘1’, the
MPR121 is in Run Mode. The MPR121 will continue to run on its own until it is set again to Stop Mode by the user.
The MPR121 registers read operation can be done at any time, either in Run Mode or in Stop Mode. However, the register write
operation can only be done in Stop Mode. The ECR (0x5E) and GPIO/LED control registers (0x73~0x7A) can be written at
anytime.
5.2
Touch Status Registers (0x00~0x01)
These two registers indicate the detected touch/release status of all of the 13 sensing input channels. ELEPROX is the status for
the 13th proximity detection channel. The update rate of these status bits will be {ESI x SFI}.
ELEx, ELEPROX: Touch or Release status bit of each respective channel (read only).
1, the respective channel is currently deemed as touched.
0, the respective channel is deemed as released.
Note: When an input is not configured as an electrode and enabled as GPIO input port, the corresponding status bit shows the
input level, but these GPIO status changes will not cause any IRQ interrupt. This feature is for ELE4~ELE11 only.
OVCF: Over Current Flag (read and write)
1, over current was detected on REXT pin.
0, normal condition.
When over current is detected, the OVCF is set to ‘1’ and the MPR121 goes to Stop Mode. All other bits in status registers
0x00~0x03, output registers 0x04~0x2A, and bits D5~D0 in ECR (0x5E) will also be cleared. When the bit is set at ‘1’, the write
to the ECR register to enter Run Mode will be discarded. The write to ’1’of the OVCF will clear this bit and the MPR121 fault
condition will be cleared. The MPR121 can then be configured to return to the Run Mode again.
ELE0-ELE7 Touch Status (0x00)
Bit
D7
D6
D5
D4
D3
D2
D1
D0
Read
ELE7
ELE6
ELE5
ELE4
ELE3
ELE4
ELE1
ELE0
Write
—
ELE8-ELE11 ELEPROX Touch Status (0x01)
Bit
D7
D6
D5
D4
D3
D2
D1
D0
Read
OVCF
—
ELEPROX
ELE11
ELE10
ELE9
ELE8
Write
—