MPR084

Sensors

20

Freescale Semiconductor

Preliminary

6.3

Buffered

The Buffered output is done through a FIFO. The FIFO will buffer every touch that occurs up to 30 values before the buffer

overflows and data is lost. Any time data is read from the FIFO it is pulled from the buffer and the next item becomes available.

The buffer can be cleared (NDF goes high) by either reading the last entry or attempting to write to the register.

The buffer settings are configured in the Touch Pad Configuration Register as described in Section 3.4.

6.3.1

FIFO Register

The FIFO Register is a read only register for determining the current status of the touch pad. Any time a write is issued to this

Figure 23. FIFO Register

6.4

Error

The MPR084 can generate a fault under two conditions; an electrode is shorted to VDD, or an electrode is shorted to VSS. Once

a fault is asserted the sensor electrodes will no longer be scanned until the fault is cleared. In the event of multiple faults occurring

at the same time, the sensor controller will report the first fault that is detected during scanning.

short, there is also a fault for when too many keys have been touched. The Max Number of Keys Exceeded status bit is an

7

6

543210

R

MDF

NDF

OF

TRF

BP

W

Reset:

0

1

000000

= Unimplemented

Table 14. FIFO Register Field Descriptions

Field

Description

7

MDF

More Data Flag – The More Data Flag shows whether or not data will remain in the

buffer after the current read.

0 No Data Remaining

1 Data Remaining

6

NDF

No Data Flag – The No Data Flag shows whether or not there is currently data in

the buffer.

0 Buffer currently has data

1 Buffer does not currently have data

5

OF

Overflow Flag – The Overflow Flag shows whether or not an overflow has occurred.

If this flag is high then the most current data was lost.

0 No Overflow has occurred

1 Overflow has occurred

4

TRF

Touch Release Flag – The Touch Release Flag shows if the current buffer entry is

a touch or release of a pad.

0 Pad is released

1 Pad is touched

3:0

BP

Buffered Position – The Buffered Position represents the electrode number that is

currently being displayed by the buffer.

0000 Encoding 0 – Buffered touch of electrode 1

~

0111 Encoding 7 – Buffered touch of electrode 8