MCP4017 datasheet(37/66 Pages) MICROCHIP

37 / 66 page

DS22147A-page 37

MCP4017/18/19

5.3

Software Reset Sequence

At times it may become necessary to perform a

Software Reset Sequence to ensure the MCP4017/18/

19 device is in a correct and known I2C Interface state.

This only resets the I2C state machine.

This is useful if the MCP4017/18/19 device powers up

in an incorrect state (due to excessive bus noise, etc),

or if the Master Device is reset during communication.

Figure 5-11 shows the communication sequence to

software reset the device.

FIGURE 5-11:

Software Reset Sequence

Format.

The 1st Start bit will cause the device to reset from a

state in which it is expecting to receive data from the

Master Device.In this mode, the device is monitoring

the data bus in Receive mode and can detect the Start

bit forces an internal Reset.

The nine bits of ‘1’ are used to force a Reset of those

devices that could not be reset by the previous Start bit.

This occurs only if the MCP4017/18/19 is driving an A

on the I2C bus, or is in output mode (from a Read

command) and is driving a data bit of ‘0’ onto the I2C

bus. In both of these cases, the previous Start bit could

not be generated due to the MCP4017/18/19 holding

the bus low. By sending out nine ‘1’ bits, it is ensured

that the device will see a A (the Master Device does not

drive the I2C bus low to acknowledge the data sent by

the MCP4017/18/19), which also forces the MCP4017/

18/19 to reset.

The 2nd Start bit is sent to address the rare possibility

of an erroneous write. This could occur if the Master

Device was reset while sending a Write command to

the MCP4017/18/19, AND then as the Master Device

returns to normal operation and issues a Start condition

while the MCP4017/18/19 is issuing an A. In this case

if the 2nd Start bit is not sent (and the Stop bit was sent)

the MCP4017/18/19 could initiate a write cycle.

The Stop bit terminates the current I2C bus activity. The

MCP4017/18/19 wait to detect the next Start condition.

This sequence does not effect any other I2C devices

which may be on the bus, as they should disregard this

as an invalid command.

5.4

Serial Commands

The MCP4017/18/19 devices support 2 serial

commands. These commands are:

• Write Operation

• Read Operations

Note:

This technique should be supported by

any I2C compliant device. The 24xxxx I2C

Serial EEPROM devices support this tech-

nique, which is documented in AN1028.

Note:

The potential for this erroneous write

ONLY occurs if the Master Device is reset

while sending a Write command to the

MCP4017/18/19.

‘1’ ‘1’ ‘1’ ‘1’ ‘1’ ‘1’ ‘1’ ‘1’

Start

bit

Nine bits of ‘1’

Start bit

Stop bit

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