TN-29-13: Determining NAND Flash Ready/Busy Status
Introduction
Technical Note
Monitoring Ready/Busy Status
in 2Gb, 4Gb, and 8Gb Micron NAND Flash Devices
For detailed NAND Flash device information, refer to www.micron.com/products/nand/.
Introduction
Systems that utilize NAND Flash memory can use either the ready/busy pin or the status
register to determine if a Micron NAND Flash device is busy or ready to accept a new
command. This technical note addresses only the use of status register bit 5, which indi-
cates the ready/busy status of the NAND Flash device. In addition to the ready/busy
status recommendations provided here, Micron also recommends making full use of
status register bits 0 and 1 to check PROGRAM and ERASE success, bit 6 to check the
cache ready/busy status, and bit 7 to check write protect status.
Four options for determining the NAND Flash ready/busy device status are presented in
this technical note. Detailed explanations of each option follow.
Monitoring Ready/Busy Status Using the R/B# Pin
Micron NAND Flash devices are equipped with a ready/busy (R/B#) pin. The system can
simply monitor this pin to determine the ready/busy status of the device. If the device is
ready to accept a new command, R/B# will be HIGH; if the device is busy, R/B# will be
LOW. This is the simplest method for determining the ready/busy status of the device;
however, some systems lack the hardware resources to support the R/B# pin. In this
case, other methods for monitoring NAND Flash device status are required.
Monitoring Ready/Busy Using the READ STATUS (70h) Command
Micron NAND Flash devices are equipped with an 8-bit status register that the system
software can read during device operation. When bit 5 of this status register is HIGH, the
device is ready; when LOW, the device is busy. To access the status register, the system
must issue the 70h command, then toggle the read enable (RE#) pin from HIGH to LOW.
Additional considerations must be taken into account when the system reads status on a
continuing basis. The following examples illustrate three different methods of moni-
toring ready/busy using the READ STATUS command.
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tn2913_ready_busy.fm - Rev. B 5/07 EN 1 ©2005 Micron Technology, Inc. All rights reserved.
Products and specifications discussed herein are for evaluation and reference purposes only and are subject to change by
Micron without notice. Products are only warranted by Micron to meet Micron’s production data sheet specifications. All
information discussed herein is provided on an “as is” basis, without warranties of any kind.
TN-29-13: Determining NAND Flash Ready/Busy Status
Monitoring Ready/Busy Using the READ STATUS (70h) Command
READ STATUS Method 1
To use this method, issue the 70h command, drive the RE# pin LOW, and then drive it
HIGH. The status register is output to the I/Os. If I/O5 is LOW, the NAND Flash device is
busy; the system toggles RE# again and rechecks I/O5. This process continues until
I/O5 = 1, indicating the NAND Flash device is ready for another command.
Figure 1: READ STATUS Method 1 Flow Chart
Issue
READ STATUS (70h)
Command
Drive RE# LOW
Read status register
output
on I/O[7:0]
Drive RE# HIGH
I/O5 = 1
Yes
Issue next
required command
No
PDF: 09005aef81d73b68 / Source: 09005aef81d73975 Micron Technology, Inc., reserves the right to change products or specifications without notice.
tn2913_ready_busy.fm - Rev. B 5/07 EN 2 ©2005 Micron Technology, Inc. All rights reserved.
TN-29-13: Determining NAND Flash Ready/Busy Status
Monitoring Ready/Busy Using the READ STATUS (70h) Command
READ STATUS Method 2
To use this method, issue the 70h command and hold the RE# pin LOW. The status
register output will continually change on the I/Os when RE# is LOW, so the user can
simply monitor the output on I/O5 and wait for it to go HIGH, after which the next
command can be issued.
Figure 2: READ STATUS Method 2 Flow Chart
Issue
READ STATUS (70h)
Command
Drive RE# LOW
Read status register
output
on I/O[7:0]
I/O5 = 1
Yes
Drive RE# HIGH
Issue next
required command
No
PDF: 09005aef81d73b68 / Source: 09005aef81d73975 Micron Technology, Inc., reserves the right to change products or specifications without notice.
tn2913_ready_busy.fm - Rev. B 5/07 EN 3 ©2005 Micron Technology, Inc. All rights reserved.
TN-29-13: Determining NAND Flash Ready/Busy Status
Monitoring Ready/Busy Using the READ STATUS (70h) Command
READ STATUS Method 3 (Not supported)
To use this method, issue the 70h command, drive the RE# pin LOW, and then drive it
HIGH. The status register is output to the I/Os. If I/O5 is LOW, the NAND Flash device is
busy; the system issues another 70h command, then toggles RE# again and rechecks
I/O5. This process continues until I/O5 = 1, indicating that the NAND Flash device is
ready for another command.
Figure 3: READ STATUS Method 3 Flow Chart
Issue
READ STATUS (70h)
Command
Drive RE# LOW
Read status register
output
on I/O[7:0]
Drive RE# HIGH
I/O5 = 1
Yes
Issue next
required command
No
PDF: 09005aef81d73b68 / Source: 09005aef81d73975 Micron Technology, Inc., reserves the right to change products or specifications without notice.
tn2913_ready_busy.fm - Rev. B 5/07 EN 4 ©2005 Micron Technology, Inc. All rights reserved.
TN-29-13: Determining NAND Flash Ready/Busy Status
Recommendations
Recommendations
Micron recommends monitoring the ready/busy status of NAND Flash devices using the
R/B# pin, as this is the simplest method and requires the least software interaction
between the system and the NAND Flash device.
Where a system lacks hardware resources to support the R/B# pin, Micron recommends
using READ STATUS Method 1 or 2. These methods require fewer system resources than
READ STATUS Method 3.
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tn2913_ready_busy.fm - Rev. B 5/07 EN 5 ©2005 Micron Technology, Inc. All rights reserved.
TN-29-13: Determining NAND Flash Ready/Busy Status
Revision History
Revision History
Rev. B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5/07
• Page 1: Updated Web link and revised description.
• “READ STATUS Method 3 (Not supported)” on page 4: Revised description.
• Former Table 1 on page 5: Deleted table.
• “Recommendations” on page 5: Revised description.
Rev. A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10/05
• Initial release.
PDF: 09005aef81d73b68 / Source: 09005aef81d73975 Micron Technology, Inc., reserves the right to change products or specifications without notice.
tn2913_ready_busy.fm - Rev. B 5/07 EN 6 ©2005 Micron Technology, Inc. All rights reserved.
Technical Note
Introduction
Monitoring Ready/Busy Status Using the R/B# Pin
Monitoring Ready/Busy Using the READ STATUS (70h) Command
READ STATUS Method 1
READ STATUS Method 2
READ STATUS Method 3 (Not supported)
Recommendations
Revision History
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