MPR084

Sensors

Freescale Semiconductor

7

Preliminary

2.3.5

The Slave Address

The MPR084 has a 7-bit long slave address (Figure 9). The bit following the 7-bit slave address (bit eight) is the R/W bit, which

is low for a write command and high for a read command.

Figure 9. Slave Address

The MPR084 monitors the bus continuously, waiting for a START condition followed by its slave address. When a MPR084

recognizes its slave address, it acknowledges and is then ready for continued communication.

2.3.6

Message Format for Writing the MPR084

A write to the MPR084 comprises the transmission of the MPR084’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 MPR084 is to be written by the next byte, if received. If a STOP condition is detected after the command byte is

received, then the MPR084 takes no further action (Figure 10) beyond storing the command byte. Any bytes received after the

command byte are data bytes.

Figure 10. Command Byte Received

Any bytes received after the command byte are data bytes. The first data byte goes into the internal register of the MPR084

Figure 11. 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

MPR084 internal registers because the command byte address generally auto-increments (Section 2.4).

2.3.7

Message Format for Reading the MPR084

The MPR084 is read using the MPR084’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 (Section 6.4.1). Thus, a read is initiated by first configuring the MPR084’s command byte by performing a write

(Figure 12). The master can now read ‘n’ consecutive bytes from the MPR084, with the first data byte being read from the register

addressed by the initialized command byte.

SDA

1

R/W

ACK

MSB

SCL

01

01

0

0

SAA

P

0

SLAVE ADDRESS

COMMAND BYTE

acknowledge from MPR084

R/W

acknowledge from MPR084

D7

D6

D5

D4

D3

D2 D1

D0

Commandbyte is storedonreceipt ofSTOP condition

SA

AA

P

0

SLAVE ADDRESS

COMMAND BYTE

DATA BYTE

acknowledge from MPR084

R/W

1byte

auto-increment memory

word address

D15 D14 D13 D12 D11 D10 D9 D8

D1 D0

D3 D2

D5 D4

D7 D6

Howcommand byte and data byte

map into MPR084's registers

acknowledge from

MPR084

acknowledge from

MPR084