MCP7940N-ESLASHMS datasheet(10/58 Pages) MICROCHIP

10 / 58 page

MCP7940N

DS20005010J-page 10

 2011-2022 Microchip Technology Inc. and its subsidiares

FIGURE 4-2:

ACKNOWLEDGE TIMING

4.1.2

DEVICE ADDRESSING

The control byte is the first byte received following the

Start condition from the host device (Figure 4-3). The

control byte begins with a 4-bit control code. For the

MCP7940N, this is set ‘1101’ for register read and

write operations. The next three bits are non-config-

urable Chip Select bits that must always be set to ‘1’.

The last bit of the control byte defines the operation to

be performed. When set to a ‘1’ a read operation is

selected, and when set to a ‘0’ a write operation is

selected.

The combination of the 4-bit control code and the three

Chip Select bits is called the client address. Upon

receiving a valid client address, the client device out-

puts an acknowledge signal on the SDA line. Depend-

ing on the state of the R/W bit, the MCP7940N will

select a read or a write operation.

FIGURE 4-3:

CONTROL BYTE FORMAT

SCL

Transmitter must release the SDA line at this point

allowing the Receiver to pull the SDA line low to

acknowledge the previous eight bits of data.

Receiver must release the SDA line at this point

so the Transmitter can continue sending data.

Data from transmitter

SDA

Acknowledge

Bit

SACK

R/W

Control Code

Chip Select

Bits

Acknowledge Bit

Start Bit

Read/Write Bit

RTCC Register/SRAM Control Byte

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