Datasheet

MCP40D17/18/19
DS22152B-page 38 © 2009 Microchip Technology Inc.
5.4.1 WRITE OPERATION
The write operation requires the START condition,
Control Byte, Acknowledge, Command Code,
Acknowledge, Data Byte, Acknowledge and STOP (or
RESTART) condition. The Control (Slave Address)
Byte requires the R/W
bit equal to a logic zero (R/W =
“0”) to generate a write sequence. The MCP40D17/
18/19 is responsible for generating the Acknowledge
(A) bits.
Data is written to the MCP40D17/18/19 after every byte
transfer (during the A bit). If a STOP or RESTART
condition is generated during a data transfer (before
the A bit), the data will not be written to MCP40D17/18/
19.
Data bytes may be written after each Acknowledge.
The command is terminated once a Stop (P) condition
occurs. Refer to Figure 5-12 for the single byte write
sequence and Figure 5-13 for the generic (multi-byte)
write sequence. For a single byte write, the master
sends a STOP or RESTART condition after the 1st data
byte is sent.
The MSb of each Data Byte is a don’t care, since the
wiper register is only 7-bits wide.
The command is terminated once a Stop (P) or Restart
(S) condition occurs.
Figure 5-14 shows the I
2
C write communication
behavior of the Master Device and the MCP40D17/18/
19 device and the resultant I
2
C bus values.
5.4.2 READ OPERATIONS
The read operation requires the START condition,
Control Byte, Acknowledge, Command Code,
Acknowledge, Restart Condition, Control Byte,
Acknowledge, Data Byte, the master generating the
A
and STOP (or RESTART) condition. The first Control
Byte requires the R/W bit equal to a logic zero (R/W =
“0”) to write the Command Code, while the second
Control Byte requires the R/W
bit equal to a logic one
(R/W = “1”) to generate a read sequence. The
MCP40D17/18/19 will A the Slave Address Byte and A
all the Data Bytes. The I
2
C Master will A the Slave
Address Byte and the last Data Byte. If there are
multiple Data Bytes, the I
2
C Master will A all Data Bytes
except the last Data Byte (which it will A).
The MCP40D17/18/19 maintains control of the SDA
signal until all data bits have been clocked out.
The command is terminated once a Stop (P) or Restart
(S) condition occurs. Refer to Figure 5-15 for the read
command sequence. For a single read, the master
sends a STOP or RESTART condition after the 1st data
byte (and A bit) is sent from the slave.
Figure 5-16 shows the I
2
C read communication
behavior of the Master Device and the MCP40D17/18/
19 device and the resultant I
2
C bus values.
FIGURE 5-12: I
2
C Single Byte Write Command Format (Slave Address = “0101110”).
Note: A command code with a non-zero value
will cause the data not to be written to the
wiper register
Note: A command code with a non-zero value
will cause the data not to be read from the
wiper register
STOP bit
Slave Address Byte
Command Code Data Byte
1010S 1100 0A000AD3XD6D5D4 D2D1D0 A
Fixed
Address
P
Read/Write bit (“0” = Write)
00 00
S = Start Condition
P = Stop Condition
A = Acknowledge
X = Don’t Care
R/W
= Read/Write bit
D6:D0 = Data bits
Legend