Datasheet

MCP9843/98243
DS22153C-page 40 © 2009 Microchip Technology Inc.
5.3.4 READ OPERATION
Read operations are initiated in the same way as write
operations, with the exception that the R/W
bit of the
slave address is set to ‘1’. There are three basic types
of read operations: current address read, random read
and sequential read.
5.3.4.1 Current Address Read
The MCP98243 contains an address counter that
maintains the address of the last word accessed,
internally incremented by ‘1’. Therefore, if the previous
access (either a read or write operation) was to
address
n, the next current address read operation
would access data from address n+1. Upon receipt of
the slave address with R/W bit set to ‘1’, the MCP98243
issues an acknowledge and transmits the 8-bit data
word. The master will not acknowledge (NAK) the
transfer but does generate a Stop condition and the
MCP98243 discontinues transmission (Figure 5-18).
FIGURE 5-18: Reading Current Word Address (See Section 4.0 “Serial Communication”).
TABLE 5-5: DEVICE RESPONSE WHEN READING SWP/CWP/PWP (NOTE)
Status Command ACK Address ACK Data Byte ACK
Not Protected SWP/CWP/PWP ACK X NoACK X NoACK
Protected with SWP
SWP NoACK X NoACK X NoACK
CWP ACK X NoACK X NoACK
PWP ACK X NoACK X NoACK
Permanently Protected SWP/CWP/PWP NoACK X NoACK X NoACK
Note: X is defined as ‘don’t care’.
1010
A
A
C
K
N
A
K
S P
2
A
1
A
0
12345678 12345678
Address Byte
Current Word Address
R
MCP98243
Master
SDA
SCL
00000
000
Note: In this example, the current word address is the
previously accessed address location n plus 1.