MCP79411 datasheet(19/38 Pages) MICROCHIP

19 / 38 page

 2011 Microchip Technology Inc.

Preliminary

DS22266B-page 19

MCP7941X

FIGURE 5-3:

EE BYTE WRITE

FIGURE 5-4:

EE PAGE WRITE

5.2.3

BLOCK PROTECTION

The EEPROM does not support a hardware write

protection pin, however, software block protection is

available to the use and is configured using the

STATUS register.

5.2.4

READ OPERATION

Read operations are initiated in the same way as write

operations with the exception that the R/W bit of the

control byte is set to one. There are three basic types

of read operations: current address read, random read,

and sequential read. The SRAM array can be read in

the same way as the EEPROM using the control byte

for the SRAM ‘1101111’ with a valid address.

5.2.4.1

Current Address Read

The MCP7941X contains an address counter that

maintains the address of the last word accessed,

internally incremented by one. Therefore, if the

previous read access was to address n (n is any legal

address), the next current address read operation

would access data from address n + 1.

Upon receipt of the control byte with R/W bit set to one,

the MCP7941X issues an Acknowledge and transmits

the 8-bit data word. The master will not acknowledge

the transfer but does generate a Stop condition and the

MCP7941X discontinues transmission (Figure 5-1).

FIGURE 5-1:

CURRENT ADDRESS READ

(EEPROM SHOWN)

5.2.4.2

Random Read

Random read operations allow the master to access

any memory location in a random manner. To perform

this type of read operation, first the word address must

be set. This is done by sending the word address to the

MCP7941X as part of a write operation (R/W bit set to

‘0’). After the word address is sent, the master

generates a Start condition following the Acknowledge.

This terminates the write operation, but not before the

internal Address Pointer is set. Then, the master issues

the control byte again but with the R/W bit set to a one.

The MCP7941X will then issue an Acknowledge and

transmit the 8-bit data word. The master will not

acknowledge the transfer but it does generate a Stop

condition which causes the MCP7941X to discontinue

transmission

(Figure 5-2).

After

random

read

command, the internal address counter will point to the

address location following the one that was just read.

BUS ACTIVITY

MASTER

SDA LINE

BUS ACTIVITY

CONTROL

BYTE

ADDRESS

BYTE

DATA

S 101 0

1 11

x = don’t care for 1K devices

BUS ACTIVITY

MASTER

SDA LINE

BUS ACTIVITY

CONTROL

BYTE

ADDRESS

BYTE

DATA BYTE 0

DATA BYTE 7

S 1 010

111

x = don’t care for 1K devices

BUS ACTIVITY

MASTER

SDA LINE

BUS ACTIVITY

CONTROL

BYTE

DATA

BYTE

11 1

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