MPR081

Sensors

Freescale Semiconductor

9

Any bytes received after the command byte are data bytes.

The first data byte goes into the internal register of the

MPR081 selected by the command byte (Figure 10).

Figure 10. Command and Single Data Byte Received

If multiple data bytes are transmitted before a STOP

condition is detected, these bytes are generally stored in

subsequent MPR081 internal registers because the

command byte address generally auto-increments (Table 8).

MESSAGE FORMAT FOR READING THE MPR081

The MPR081 is read using the MPR081's internally stored

command byte as address pointer, the same way the stored

command byte 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 (Table 11). Thus, a read is

initiated by first configuring the MPR081's command byte by

performing a write (Figure 9). The master can now read 'n'

consecutive bytes from the MPR081, with the first data byte

being read from the register addressed by the initialized

command byte. When performing read-after-write

verification, remember to re-set the command byte's address

because the stored command byte address will generally

have been auto-incremented after the write (Table 8).

Figure 11. ‘n’ Data Bytes Received

OPERATION WITH MULTIPLE MASTERS

If the MPR081 is operated on a 2-wire interface with

multiple masters, a master reading the MPR081 should use

repeated start(s) between the write(s) which sets the

MPR081's address pointer, and the read(s) that take the data

from the location(s). This is because it is possible for master

#2 to take over the bus after master #1 has set up the

MPR081's address pointer, but before master #1 has read

the data. If master #2 subsequently re-sets the master of the

MPR08's address pointer, then master #1's read may be from

an unexpected location.

DEVICE RESET

The reset input RST is an active-low input. When taken

low, RST clears any transaction to or from the MPR081 on

the serial interface and configures the internal registers to the

same state as a power-up reset (Table 9). The MPR081 then

waits for a START condition on the serial interface.

CONTROLLING AND READING THE MPR081

REGISTER ORGANIZATION

The MPR081 is a peripheral that is controlled and

monitored though a small array of internal registers which are

INITIAL POWER-UP

On power-up, the interrupt output IRQ is reset, and IRQ

will go high. The registers are reset to the values shown in

Table 9.

STANDBY MODE

When the serial interface is idle, the MPR081

automatically enters standby mode. If any of the features are

used, the operating current rises because the internal timing

oscillator is running and toggling counters.

Figure 12. Master Tick Counter and

Pad/Key Input Sampling with Autorepeat