Datasheet

CKE Truth Table
(a) Note 1~7 apply to the entire Command truth table
(b) CKE low is allowed only if tMRD and tMOD are satisfied
Notes:
1. CKE (N) is the logic state of CKE at clock edge N; CKE (N–1) was the state of CKE at the previous clock edge.
2. Current state is defined as the state of the DDR3 SDRAM immediately prior to clock edge N
3. COMMAND (N) is the command registered at clock edge N, and ACTION (N) is a result of COMMAND (N), ODT is not included here
4. All states and sequences not shown are illegal or reserved unless explicitly described elsewhere in this document
5. The state of ODT does not affect the states described in this table. The ODT function is not available during Self Refresh
6. CKE must be registered with the same value on tCKEmin consecutive positive clock edges. CKE must remain at the valid input level the entire time it
takes to achieve the tCKEmin clocks of registeration. Thus, after any CKE transition, CKE may not transition from its valid level during the time period
of tIS + tCKEmin + tIH.
7. DESELECT and NOP are defined in the Command truth table
8. On Self Refresh Exit DESELEC
T or NOP commands must be issued on every clock edge occurring during the tXS period. Read or ODT commands
may be issued only after tXSDLL is satisfied.
9. Self Refresh mode can only be entered from the All Banks Idle state.
10. Must be a legal command as defined in the Command Truth Table.
11. Valid commands for Power Down Entry and Exit are NOP and DESELECT only.
12. Valid commands for Self Refresh Exit are NOP and DESELECT only.
13. Self Refresh can not be entered while Read or Write operations. See ‘Self-Refresh Operation” and ‘Power-Down Modes” on
detailed list of restrictions.
14. The Power Down does not perform any refresh operations.
15. “X” means “don’t care (including floating around V
REF
)” in Self Refresh and Power Down. It also applies to Address pins
16. V
REF
(Both V
REFDQ
and V
REFCA
) must be maintained during Self Refresh operation.
17. If all banks are closed at the conclusion of the read, write or precharge command, then Precharge Power Down is entered, otherwise Active Power
Down is entered
18. ‘Idle state’ means that all banks are closed(tRP,tDAL,etc. satisfied) and CKE is high and all timings from previous operations are satisfied
(tMRD,tMOD,tRFC,tZQinit,tZQoper,tZQCS,etc)as well as all SRF exit and Power Down exit parameters are satisfied (tXS,tXP,tXPDLL,etc)
Current State
2
CKE
Command (N)
3
RAS, CAS, WE, CS
Action (N)
3
Notes
Previous Cycle
1
(N-1)
Current Cycle
1
(N)
Power Down
L L X Maintain Power-Down 14, 15
L H DESELECT or NOP Power Down Exit 11, 14
Self Refresh
L L X Maintain Self Refresh 15, 16
L H DESELECT or NOP Self Refresh Exit 8, 12, 16
Bank(s) Active H L DESELECT or NOP Active Power Down Entry 11, 13, 14
Reading H L DESELECT or NOP Power Down Entry 11, 13, 14, 17
Writing H L DESELECT or NOP Power Down Entry 11, 13, 14, 17
Precharging H L DESELECT or NOP Power Down Entry 11, 13, 14, 17
Refreshing H L DESELECT or NOP Precharge Power Down Entry 11
All Banks Idle
H L DESELECT or NOP Precharge Power Down Entry 11,13, 14, 18
H L REFRESH Self Refresh Entry 9, 13, 18
For more details with all signals See “Command Truth Table,” on previous page
10
later section for a
AS4C256M16D3B-12BIN
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Rev.1.1 April 2017