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DS21125E-page 8

 2004 Microchip Technology Inc.

byte would be 10XX0011. After the third byte is sent to

the device, it will acknowledge and a STOP bit is then

sent by the master to complete the command.

During a normal write sequence, if an attempt is made

to write to a protected address, no data will be written

and the device will not report an error or abort the

command. If a write command is attempted across a

secure boundary, unprotected addresses will be written

and protected addresses will not.

5.8

Security Configuration Read

The status of the secure portion of memory can be read

by using the same technique as programming this

option except the READ bit (bit 6) of the configuration

byte is set to a one. After the configuration byte is sent,

the device will acknowledge and then send two bytes of

data to the master just as in a normal read sequence.

The master must acknowledge the first byte and not

acknowledge the second, and then send a stop bit to

end the sequence. The upper four bits of both of these

bytes will always be read as '1's. The lower four bits of

the first byte contains the starting secure block. The

lower four bits of the second byte contains the number

of secure blocks. The default starting secure block is

fifteen and the default number of secure blocks is zero

(Figure 8-1).

6.0

ACKNOWLEDGE POLLING

Since the device will not acknowledge during a write

cycle, this can be used to determine when the cycle is

complete (this feature can be used to maximize bus

throughput). Once the STOP for a write command has

been issued from the master, the device initiates the

internally timed write cycle. ACK polling can be initiated

immediately. This involves the master sending a

START followed by the control byte for a write

command (R/W = 0). If the device is still busy with the

write cycle, then no ACK will be returned. If the cycle is

complete, then the device will return the ACK and the

master can then proceed with the next read or write

command. See Figure 6-1 for flow diagram.

FIGURE 6-1:

ACKNOWLEDGE POLLING

FLOW

Did Device

Acknowledge

(ACK = 0)?

Send

Write Command

Send Stop

Condition to

Initiate Write Cycle

Send Start

Send Control Byte

with R/W = 0

Next

Operation

No

Yes