MCP47FXB2XT-EST datasheet(83/124 Pages) MICROCHIP

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DS20006368A-page 83

MCP47FXBX4/8

7.2

READ Command

(Normal and High-Voltage)

READ commands are used to transfer data from the

specified memory location to the host controller. The

READ command can be issued to both volatile and

nonvolatile memory locations.

During an EEPROM write cycle (write to nonvolatile

memory location or Enable/Disable Configuration Bit

command) the READ command can only read the vola-

tile memory locations. By reading the STATUS register

(0Ah), the host controller can determine when the write

cycle has been completed (via the state of the EEWA

bit).

The READ command formats include:

• Single Read

- Single Memory Address

- Last Memory Address Accessed

• Continuous Reads

The MCP47FXBX4/8 retains the last device memory

address received. That is the MCP47FXBX4/8 does

not corrupt the device memory address after repeated

Start or Stop conditions.

If the address pointer is for a nonvolatile memory

location during a nonvolatile write cycle (tWC), the

MCP47FXBX4/8 will respond with an A bit.

7.2.1

SINGLE READ

The READ command format writes two bytes, the

Control byte and the READ command byte (desired

memory address and the READ command), and then

has a Restart condition. Then, a 2nd Control byte is

transmitted, but this control byte indicates an I2C read

operation (R/W bit = ‘1’).

7.2.1.1

Single Memory Address

Figure 7-4 shows the sequence for reading a specified

memory address.

7.2.1.2

Last Memory Address Accessed

Figure 7-5 shows the waveforms for a single read of

the last memory location accessed.

This command allows faster communication when

checking the status of the EEPROM Write Active

(EEWA) bit (see Register 4-4), as long as the register

address of the device’s last command is 0Ah.

7.2.2

CONTINUOUS READS

Continuous reads allow the device’s memory to be

read quickly. Continuous reads are possible to all

memory locations. If a nonvolatile memory write cycle

occurs, then READ commands may only access the

volatile memory locations.

Figure 7-7 shows the sequence for three continuous

reads.

For continuous reads, instead of transmitting a Stop or

Restart condition after the data transfer, the master

continually reads the data byte. The sequence ends

with the master Not Acknowledging and then sending a

Stop or Restart.

This is useful in reading the System STATUS register

(0Ah) to determine if an EEPROM write cycle has been

completed (EEWA bit).

7.2.3

IGNORING AN I2C TRANSMISSION

AND “FALLING OFF” THE BUS

The MCP47FXBX4/8 expects to receive complete,

valid I2C commands and will assume any command not

defined as a valid command. This is due to a bus

corruption, thus entering a passive High condition on

the SDA signal. All signals will be ignored until the next

valid Start condition and Control byte are received.

Note 1: During device communication, if the

device address/command combination is

invalid or an unimplemented address is

specified, then the MCP47FXBX4/8 will

NACK that byte. To reset the I2C state

machine, the I2C communication must

detect a Start bit.

2: If the LAT pin is high (VIH), reads of the

volatile DAC register read the output

value, not the internal register.

3: READ commands operate the same

regardless of the state of the High-

Voltage command signal.

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