MT40A256M16GE-075EAUT Datasheet, PDF (136/359 Pages) Micron Technology – Automotive DDR4 SDRAM

4Gb: x8, x16 Automotive DDR4 SDRAM
REFRESH Command
FI (Figure 79 (page 136)), 18 × ^tRFEI2, or 36 × ^tREFI4. At any given time, a maximum of
16 REF commands can be issued within 2 × ^tREFI, 32 REF2 commands can be issued
within 4 × ^tREFI2, and 64 REF4 commands can be issued within 8 × ^tREFI4.
Figure 77: REFRESH Command Timing
T0
CK_c
CK_t
Command
REF
T1
DES
DES
t_RFC
DRAM must be idle
Ta0
REF
Ta1
DES
DES
t_{RFC (MIN)}
Tb0
Tb1
Tb2
Valid
Valid
Valid
t_{REFI (MAX 9 ×} t_REFI)
Tb3
Valid
Tc0
Tc1
Tc2
Tc3
Valid
REF
Valid
Valid
Valid
DRAM must be idle
Time Break
Don’t Care
Notes:
1. Only DES commands are allowed after a REFRESH command is registered until ^tRFC
(MIN) expires.
2. Time interval between two REFRESH commands may be extended to a maximum of 9 ×
t_REFI.
Figure 78: Postponing REFRESH Commands (Example)
9 × ^tREFI
t_REFI
W
t_RFC
Figure 79: Pulling In REFRESH Commands (Example)
t_REFI
t_RFC
8 REF-Commands postponed
9 × ^tREFI
W
8 REF-Commands pulled-in
CCMTD-1725822587-10418
4gb_auto_ddr4_sdram_z90b.pdf - Rev. D 01/17 EN
136
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