X9470 datasheet(24/25 Pages) XICOR

24 / 25 page

Preliminary Information

X9470

24 of 25

REV 11.16 3/20/03

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Figure 15. Acknowledge Polling Sequence

It should be noted that the ninth clock cycle of the read

operation is not a “don’t care.” To terminate a read

operation, the master must either issue a stop condi-

tion during the ninth cycle or hold SDA HIGH during

the ninth clock cycle and then issue a stop condition.

Random Read

Random read operations allows the master to access

any location in the X9470. Prior to issuing the Slave

Address Byte with the R/W bit set to zero, the master

must ﬁrst perform a “dummy” write operation.

The master issues the start condition and the slave

address byte, receives an acknowledge, then issues

the word address bytes. After acknowledging receipt of

each word address byte, the master immediately

issues another start condition and the slave address

byte with the R/W bit set to one. This is followed by an

acknowledge from the device and then by the eight bit

data word. The master terminates the read operation

by not responding with an acknowledge and then issu-

ing a stop condition. Refer to Figure 13 for the address,

acknowledge, and data transfer sequence.

In a similar operation called “Set Current Address,” the

device sets the address if a stop is issued instead of

the second start shown in Figure 14. The X9470 then

goes into standby mode after the stop and all bus

activity will be ignored until a start is detected. This

operation loads the new address into the address

counter. The next Current Address Read operation will

read from the newly loaded address. This operation

could be useful if the master knows the next address it

needs to read, but is not ready for the data.

ACK

returned?

Issue Slave

Address Byte

(Read or Write)

Byte load completed

by issuing STOP.

Enter ACK Polling

Issue STOP

Issue START

YES

Issue STOP

Continue normal

Read or Write

command

sequence

PROCEED

YES

nonvolatile write

Cycle complete.

Continue command

sequence?

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