Datasheet

© 2009 Microchip Technology Inc. DS22152B-page 35
MCP40D17/18/19
5.2.5 STOP BIT
The Stop bit (see Figure 5-6) Indicates the end of the
I
2
C Data Transfer Sequence. The Stop bit is defined as
the SDA signal rising when the SCL signal is “High”.
A Stop bit resets the I
2
C interface of the other devices.
FIGURE 5-6: Stop Condition Receive or
Transmit Mode.
5.2.6 CLOCK STRETCHING
“Clock Stretching” is something that the Secondary
Device can do, to allow additional time to “respond” to
the “data” that has been received.
The MCP40D17/18/19 will not strech the clock signal
(SCL) since memory read accesses occur fast enough.
5.2.7 ABORTING A TRANSMISSION
If any part of the I
2
C transmission does not meet the
command format, it is aborted. This can be intentionally
accomplished with a START or STOP condition. This is
done so that noisy transmissions (usually an extra
START or STOP condition) are aborted before they
corrupt the device.
5.2.8 IGNORING AN I
2
C TRANSMISSION
AND “FALLING OFF” THE BUS
The MCP40D17/18/19 expects to receive entire, valid
I
2
C commands and will assume any command not
defined as a valid command is due to a bus corruption
and will enter a passive high condition on the SDA
signal. All signals will be ignored until the next valid
START condition and CONTROL BYTE are received.
FIGURE 5-7: Typical 16-bit I
2
C Waveform Format.
FIGURE 5-8: I
2
C Data States and Bit Sequence.
SCL
SDA
A / A
P
1st
SDA
SCL
S 2nd 3rd 4th 5th 6th 7th 8th PA/A
Bit Bit Bit Bit Bit Bit Bit Bit
1st 2nd 3rd 4th 5th 6th 7th 8th A/A
Bit Bit Bit Bit Bit Bit Bit Bit
SCL
SDA
START
Condition
STOP
Condition
Data allowed
to change
Data or
A valid