MB85AS8MT

DS501-00060-2v2-E

13

2. WIP polling

After the last writing data was input, writing to the nonvolatile memory needs tWC waiting time from the rising

edge of CS. This tWC time becomes larger than a minimum clock cycle. Production variation and operating

condition are considered, and this maximum tWC value is defined. In the usual operation, this tWC time is

shorter than the maximum value. Therefore, MB85AS8MT supports WIP polling to improve memory access

by optimizing the waiting time.

After starting the data writing to nonvolatile memory, MB85AS8MT sets “1” to a volatile register related to

the WIP bit in status register. After finished the writing operation, reset this WIP bit from “1” to “0”. Although

the usual commands are not executable during this writing process, only the RDSR command is acceptable.

RDSR command outputs the value of status register to SO. It is possible to confirm if the internal writing

operation to nonvolatile memory is finished or not, by checking the corresponding bit to WIP in output data

from SO.

RDSR command also outputs the WPEN, BP1 and BP0 of status register to SO. In the polling after WRSR

command, MB85AS8MT outputs the WPEN, BP1 and BP0 data which is set before the writing to nonvolatile

memory is completed. On the other hand for WEL and WIP, MB85AS8MT outputs (WEL,WIP)=2'b11 when

the writing to nonvolatile memory is not completed. When it is competed, outputs (WEL,WIP)=2'b00.

If continuously sending clocks to SCK during CS = low, it is also possible to keep on outputting WPEN to

WIP bits in status register in unit of 8 cycles since 17th clock. In case the WIP polling is applied, WIP and

WEL bits in status register output to SO by RDSR command are updated regularly.

Figure shows the example of RDSR command input with continuously sending clocks over 17 during CS =

low, before the writing process of WRSR command is finished.

CS

SCK

SI

WPEN

XXX BP1 BP0 XX

SO

busy

wip

wel

WRSR

RDSR

WPEN

X

BP1

XX

BP0

WEL

WIP

WPEN

X

BP1

XX

BP0

WEL

WIP

(Write process situation)

(Internal volatile register for WIP)

(Internal volatile register for WEL)