Winbond Electronics W981216AH Datasheet

W981216AH

2M x 16 bit x 4 Banks SDRAM

Features

• 3.3V±0.3V power supply

• Up to 133 MHz clock frequency

• 2,097,152 words x 4 banks x 16 bits organization

• Auto Refresh and Self Refresh

• CAS latency: 2 and 3

• Burst Length: 1, 2, 4, 8 , and full page

• Burst read, Single Writes Mode

• Byte data controlled by UDQM and LDQM

• Power-Down Mode

• Auto-Precharge and controlled precharge

• 4k refresh cycles / 64ms

• Interface: LVTTL

• Package: TSOP II 54 pin, 400 mil - 0.80

General Description

W981216AH is a high speed synchronous dynamic random access memory (SDRAM) , organized as 2M words x 4 banks x
16 bits. Using pipelined architecture and 0.20um process technology, W981216AH delivers a data bandwidth of up to 266M
bytes per second (-75). To fully comply to the personal computer industrial standard, W981216AH is sorted into two speed
grades: -75 and -8H. The -75 is compliant to the PC133/CL3 specification, the –8H is compliant to PC100/CL2 specification.

Accesses to the SDRAM are burst oriented. Consecutive memory location in one page can be accessed at a burst length of
1, 2, 4, 8 or full page when a bank and row is selected by an ACTIVE command. Column addresses are automatically generated
by the SDRAM internal counrter in burst operation. Random column read is also possible by providing its address at each clock
cycle. The multiple bank nature enables interleaving among internal banks to hide the precharging time.

By having a programmable Mode Register, the system can change burst legnth, latency cycle, interleave or sequential burst
to maximize its performance. W981216AH is ideal for main memory in high performance applications.

Key Parameters

Symbol Description min/max -75 (PC133) -8H (PC100)

tCK Clock Cycle Time min 7.5ns 8ns
tAC Access Time from CLK max 5.4ns 6ns

tRP Precharge to Active Command min 20ns 20ns
tRCD Active to Read/Write Command min 20ns 20ns
ICC1 Operation Current ( Single bank ) max 85mA 80mA
ICC4 Burst Operation Current max 120mA 110mA
ICC6 Self-Refresh Current max 2mA 2mA

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BLOCK DIAGRAM

W981216AH

2M x 16 bit x 4 Banks SDRAM

A10

A0

A9
A11
BS0
BS1

CLK

CKE

CS

RAS

CAS

WE

CLOCK

BUFFER

COMMAND

DECODER

ADDRESS

BUFFER

REFRESH
COUNTER

CONTROL

SIGNAL

GENERATOR

MODE

REGISTER

COLUMN

COUNTER

COLUMN DECODER

CELL ARRAY

BANK #0

ROW DECODER

SENSE AMPLIFIER

DATA CONTROL

CIRCUIT

COLUMN DECODER

CELL ARRAY

BANK #1

ROW DECODERROW DECODER

SENSE AMPLIFIER

DMn

DQ

BUFFER

DQ0

DQ15

UDQM

LDQM

COLUMN DECODER

CELL ARRAY

BANK #2

ROW DECODER

SENSE AMPLIFIER

COLUMN DECODER

CELL ARRAY

BANK #3

SENSE AMPLIFIER

NOTE:
The cell array configuration is 4096 * 512 * 16.

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W981216AH

2M x 16 bit x 4 Banks SDRAM

Pin Assignment

Pin Number Pin Name Function Description

23 ~ 26, 22,
29 ~35
20, 21 BS0, BS1 Bank Select Select bank to activate during row address latch time, or bank to

2, 4, 5, 7, 8,
10, 11, 13,
42, 44, 45,
47, 48, 50,
51, 53
19 CS# Chip Select Disable or enable the command decoder. When command

18 RAS# Row Address
17 CAS# Column
16 WE# Write Enable Referred to RAS#

39, 15 UDQM/

38 CLK Clock Inputs System clock used to sample inputs on the rising edge of clock.
37 CKE Clock Enable CKE controls the clock activation and deactivation. When CKE

1, 14, 27 VCC Power ( +3.3 V ) Power for input buffers and logic circuit inside DRAM.
28, 41, 54 VSS Ground Ground for input buffers and logic circuit inside DRAM.
3, 9, 43, 49 VCCQ Power ( + 3.3 V

6, 12, 46, 52 VSSQ Ground for I/O
36, 40 NC No Connection No connection

A0~ A11 Address Multiplexed pins for row and column address.

Row address : A0 ~ A11. Column address: A0 ~ A8.

read/write during address latch time.
DQ0 ~
DQ15

LDQM

Data Input/
Output

Strobe
Address Strobe
input/output

mask

) for I/O buffer
buffer

Multiplexed pins for data output and input.

decoder is disabled, new command is ignored and previous

operation continues.

Command input. When sampled at the rising edge of the clock,

RAS#, CAS# and WE# define the operation to be executed.

Referred to RAS#

The output buffer is placed at Hi-Z(with latency of 2) when DQM

is sampled high in read cycle. In write cycle, sampling DQM

high will block the write operation with zero latency.

is low, Power Down mode, Suspend mode, or Self Refresh

mode is entered.

Separated power from VCC, used for output buffers to improve

noise.

Separated ground from VSS, used for output buffers to improve

noise.

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Pin Assignment (Top View)

W981216AH

2M x 16 bit x 4 Banks SDRAM

VCC

DQ0

VCCQ

DQ1

DQ2

VSSQ

DQ3

DQ4

VCCQ

DQ5

DQ6

VSSQ

DQ7

VCC

LDQM

WE

CAS

RAS

CS

BS0

BS1

A10/AP

A0

A1

A2

A3

VCC

VSS

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

54

DQ15

53

VSSQ

52

DQ14

51

DQ13

50

VCCQ

49

DQ12

48

DQ11

47

VSSQ

46

DQ10

45

DQ9

44

VCCQ

43

DQ8

42

VSS

41

NC

40

UDQM

39

CLK

38

CKE

37

NC

36

A11

35

A9

34

A8

33

A7

32

A6

31

A5

30

A4

29

VSS

28

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W981216AH

2M x 16 bit x 4 Banks SDRAM

ABSOLUTE MAXIMUM RATINGS

SYMBOL ITEM RATING UNIT NOTES

VIN,VOUT Input, Output Voltage -0.3~VCC+0.3 V 1

VCC,VCCQ Power Supply Voltage -0.3~4.6 V 1

TOPR Operating Temperature 0~70
TSTG Storage Temperature -55~150

TSOLDER Soldering Temperature(10s) 260

PD Power Dissipation 1 W 1

IOUT Short Circuit Output Current 50 MA 1

RECOMMENDED DC OPERATING CONDITIONS ( Ta = 0 to 70°C )

SYMBOL PARAMETER MIN TYP MAX UNIT NOTES

VCC Power Supply Voltage 3.0 3.3 3.6 V 2

VCCQ Power Supply Voltage (for I/O Buffer) 3.0 3.3 3.6 V 2

VIH Input High Voltage 2.0 - VCC+0.3 V 2
VIL Input Low Voltage -0.3 - 0.8 V 2

°C
°C
°C

1
1
1

Note: VIH(max) = VCC/VCCQ+1.2V for pulse width < 5ns

VIL(min) = VSS/VSSQ-1.2V for pulse width < 5ns

CAPACITANCE (VCC=3.3V, Af = 1MHz, Ta=25°C)

SYMBOL PARAMETER MIN MAX UNIT

CI

CO Input/Output capacitance - 6.5 pf

Note: These parameters are periodically sampled and not 100% tested.

Input Capacitance (A0 to A11, BS0 ,BS1, CS, RAS, CAS, WE, DQM, CKE) - 4 pf
Input Capacitance (CLK) - 4 pf

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2M x 16 bit x 4 Banks SDRAM

AC CHARACTERISTICS AND OPERATING CONDITION

(Vcc=3.3V±0.3V, Ta=0° to 70°C Notes:5, 6, 7, 8)

W981216AH

SYMBOL PARAMETER

tRC Ref/Active to Ref/Active Command Period 65 68
tRAS Active to precharge Command Period 45 100000 48 100000 ns
tRCD Active to Read/Write Command Delay Time 20 20
tCCD Read/Write(a) to Read/Write(b)Command Period 1 1 cycle

tRP Precharge to Active Command Period 20 20
tRRD Active(a) to Active(b) Command Period 15 20

tWR Write Recovery Time CL*=2 10 10

CL*=3 7.5 8

tCK CLK Cycle Time CL*=2 10 1000 10 1000

CL*=3 7.5 1000 8 1000
tCH CLK High Level width 2.5 3
tCL CLK Low Level width 2.5 3
tAC Access Time from CLK CL*=2 6 6

CL*=3 5.4 6 ns
tOH Output Data Hold Time 2.7 3
tHZ Output Data High Impedance Time 2.7 7.5 3 8

tLZ Output Data Low Impedance Time 0 0

tSB Power Down Mode Entry Time 0 7.5 0 8

tT Transition Time of CLK (Rise and Fall) 0.5 10 0.5 10
tDS Data-in Set-up Time 1.5 2
tDH Data-in Hold Time 0.8 1
tAS Address Set-up Time 1.5 2
tAH Address Hold Time 0.8 1

tCKS CKE Set-up Time 1.5 2
tCKH CKE Hold Time 0.8 1
tCMS Command Set-up Time 1.5 2

tCMH Command Hold Time 0.8 1

tREF Refresh Time 64 64 ms
tRSC Mode register Set Cycle Time 15 16 ns

-75 (PC133) -8H (PC100)

MIN MAX MIN MAX

UNIT

(CL=CAS Latency)

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2M x 16 bit x 4 Banks SDRAM

DC CHARACTERISTICS (VCC = 3.3V ± 0.3V, Ta=0°~70°C)

ITEMS SYMBOL

OPERATING CURRENT
tCK=min , tRC=min
Active Precharge command cycling
without Burst operation

STANDBY CURRENT
tCK=min , CS#=VIH
VIH/L=VIH(min)/VIL(max)
Bank : inactive state
STANDBY CURRENT
CLK=VIL , CS#=VIH
VIH/L=VIH(min)/VIL(max)
BANK : inactive state

NO OPERATING CURRENT
tCK=min
CS#=VIH(min)
BANK : active state (4 banks)

BURST OPERATING CURRENT
tCK = min
Read / Write command cycling
AUTO REFRESH CURRENT
tCK = min
Auto Refresh command cycling
SELF REFRESH CURRENT
Self Refresh mode
CKE = 0.2V

1 bank operation ICC1 85 80 3

CKE = VIH ICC2 45 40 3
CKE = VIL (Power Down mode) ICC2P 1 1 3
CKE = VIH ICC2S 10 10
CKE = VIL (Power Down mode) ICC2PS 1 1 mA

CKE = VIH ICC3 50 45

CKE= VIL (Power Down mode) ICC3P 10 10

ICC4 120 110 3,4

ICC5 190 180 3

ICC6 2 2

MIN. MAX. MIN. MAX.

W981216AH

-75 (PC133) -8H (PC100)
UNIT NOTES

ITEM SYMBOL

INPUT LEAKAGE CURRENT
( 0V ≤ VIN ≤ VCC , all other pins not under test = 0V )
OUTPUT LEAKAGE CURRENT
( Output disable , 0V ≤ VOUT ≤ VCCQ )
LVTTL OUTPUT ″H″ LEVEL VOLTAGE
( IOUT = -2mA )
LVTTL OUTPUT ″L″ LEVEL VOLTAGE
( IOUT = 2mA )

MIN. MAX.

II(L)

IO(L) -5 5
VOH 2.4 - V
VOL - 0.4 V

-5 5

UNIT NOTES

µA
µA

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NOTES:

W981216AH

2M x 16 bit x 4 Banks SDRAM

1. Operation exceeds "ABSOLUTE MAXIMUM RATING" may cause permanent damage to the devices.

2. All voltages are referenced to VSS

3. These parameters depend on the cycle rate and listed values are measured at a cycle rate with the minimum values of

tCK and tRC.

4. These parameters depend on the output loading conditions. Specified values are obtained with output open.

5. Power up sequence is further described in the "Functional Description" section.

6. AC TESTING CONDITIONS

Output Reference Level 1.4V/1.4V

Output Load See diagram B below

Input Signal Levels 2.4V/0.4V

Transition Time (Rise and Fall) of Input Signal 2ns

Input Reference Level 1.4V

3.3 V

1.2K

output

50pF

0.87K

AC TEST LOAD (A)

7. Transition times are measured between VIH and VIL.

8. tHZ defines the time at which the outputs achieve the open circuit condition and is not referenced to output level.

Z = 50 ohmsoutput

AC TEST LOAD (B)

1.4 V

50 ohms

50pF

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W981216AH

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2M x 16 bit x 4 Banks SDRAM

Operation Mode

Fully synchronous operations are performed to latch the commands at the positive edges of CLK. Table 1 shows the truth
table for the operation commands.

Table 1 Truth Table ( note (1) , (2) )

command

Bank Active Idle

Bank Precharge Any

Precharge All Any

Write Active (3)

Write with Autoprecharge Active (3)

Read Active (3)

Read with Autoprecharge Active (3)

Mode Register Set Idle

No - Operation Any

Burst Stop Active (4)

Device Deselect Any

Auto - Refresh Idle

Self - Refresh Entry Idle

Self Refresh Exit idle

Clock suspend Mode Entry Active

Power Down Mode Entry Idle

Clock Suspend Mode Exit Active

Power Down Mode Exit Any

Data write/Output Enable Active

Data Write/Output Disable Active

Device state

(S.R.)

Active (5)

(power down)

CKEn-1 CKEn DQM BS0,1 A10

A11,

A9-0

CS RA CAS WE

H x x v v v L L H H
H x x v L x L L H L
H x x x H x L L H L
H x x v L v L H L L
H x x v H v L H L L
H x x v L v L H L H
H x x v H v L H L H
H x x v v v L L L L
H x x x x x L H H H
H x x x x x L H H L
H x x x x x H x x x
H H x x x x L L L H
H L x x x x L L L H
L

H L x x x x x x x x
H

L H x x x x x x x x
L

H x L x x x x x x x
H x H x x x x x x x

Notes: (1) v= valid x = Don't care L= Low Level H= High Level
(2) CKEn signal is input level when commands are provided.
(3) These are state of bank designated by BS0, BS1 signals.
(4) Device state is full page burst operation.
(5) Power Down Mode can not be entered in the burst cycle.
When this command asserts in the burst cycle, device state is clock suspend mode.

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W981216AH

2M x 16 bit x 4 Banks SDRAM

Functional Description

Power Up and Initialization

The default power up state of the mode register is unspecified. The following power up and initialization sequence need to be
followed to guarantee the device being preconditioned to each user specific needs.
During power up, all VCC and VCCQ pins must be ramp up simultaneously to the specified voltage when the input signals are held
in the "NOP" state. The power up voltage must not exceed VCC+0.3V on any of the input pins or VCC supplies. After power up,
an initial pause of 200us is required followed by a precharge of all banks using the precharge command. To prevent data
contention on the DQ bus during power up, it is required that the DQM and CKE pins be held high during the initial pause
period. Once all banks have been precharged, the Mode Register Set Command must be issued to initialize the Mode Register.
An additional eight Auto Refresh cycles (CBR) are also required before or after programming the Mode Register to ensure
proper subsequent operation.

Programming Mode Register

After initial power up, the Mode Register Set Command must be issued for proper device operation. All banks must be in a
precharged state and CKE must be high at least one cycle before the Mode Register Set Command can be issued. The Mode
Register Set Command is activated by the low signals of RAS, CAS, CS and WE at the positive edge of the clock. The address
input data during this cycle defines the parameters to be set as shown in the Mode Register Operation table. A new command
may be issued following the mode register set command once a delay equal to tRSC has elapsed. Please refer to the next page for
Mode Register Set Cycle and Operation Table.

Bank Activate Command

The Bank Activate command must be applied before any Read or Write operation can be executed. The operation is similar to
RAS# activate in EDO DRAM. The delay from when the Bank Activate command is applied to when the first read or write
operation can begin must not be less than the RAS to CAS delay time (tRCD). Once a bank has been activated it must be
precharged before another Bank Activate command can be issued to the same bank. The minimum time interval between
successive Bank Activate commands to the same bank is determined by the RAS cycle time of the device (tRC). The minimum
time interval between interleaved Bank Activate commands (Bank A to Bank B and vice versa) is the Bank to Bank delay time
(tRRD). The maximum time that each bank can be held active is specified as tRAS(max).

Read and Write Access Modes

After a bank has been activated , a read or write cycle can be followed. This is accomplished by setting RAS high and CAS low
at the clock rising edge after minimum of tRCD delay. WE pin voltage level defines whether the access cycle is a read operation
(WE high), or a write operation (WE low). The address inputs determine the starting column address.
Reading or writing to a different row within an activated bank requires the bank be precharged and a new Bank Activate
command be issued. When more than one bank is activated, interleaved bank Read or Write operations are possible. By using
the programmed burst length and alternating the access and precharge operations between multiple banks, seamless data access
operation among many different pages can be realized. Read or Write Commands can also be issued to the same bank or
between active banks on every clock cycle.

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W981216AH

2M x 16 bit x 4 Banks SDRAM

Burst Read Command

The Burst Read command is initiated by applying logic low level to CS and CAS while holding RAS and WE high at the rising
edge of the clock. The address inputs determine the starting column address for the burst. The Mode Register sets type of burst
(sequential or interleave) and the burst length (1, 2, 4, 8, full page) during the Mode Register Set Up cycle. Table 2 and 3 in the
next page explain the address sequence of interleave mode and sequence mode.

Burst Command

The Burst Write command is initiated by applying logic low level to CS, CAS and WE while holding RAS high at the rising
edge of the clock. The address inputs determine the starting column address. Data for the first burst write cycle must be applied
on the DQ pins on the same clock cycle that the Write Command is issued. The remaining data inputs must be supplied on each
subsequent rising clock edge until the burst length is completed. Data supplied to the DQ pins after burst finishes will be
ignored.

Read Interrupted by a Read

A Burst Read may be interrupted by another Read Command. When the previous burst is interrupted, the remaining addresses
are overridden by the new read address with the full burst length. The data from the first Read Command continues to appear on
the outputs until the CAS latency from the interrupting Read Command the is satisfied.

Read Interrupted by a Write

To interrupt a burst read with a Write Command, DQM may be needed to place the DQs (output drivers) in a high impedance
state to avoid data contention on the DQ bus. If a Read Command will issue data on the first and second clocks cycles of the
write operation, DQM is needed to insure the DQs are tri-stated. After that point the Write Command will have control of the
DQ bus and DQM masking is no longer needed.

Write Interrupted by a Write

A burst write may be interrupted before completion of the burst by another Write Command. When the previous burst is
interrupted, the remaining addresses are overridden by the new address and data will be written into the device until the
programmed burst length is satisfied.

Write Interrupted by a Read

A Read Command will interrupt a burst write operation on the same clock cycle that the Read Command is activated. The DQs
must be in the high impedance state at least one cycle before the new read data appears on the outputs to avoid data contention.
When the Read Command is activated, any residual data from the burst write cycle will be ignored.

Burst Stop Command

A Burst Stop Command may be used to terminate the existing burst operation but leave the bank open for future Read or Write
Commands to the same page of the active bank, if the burst length is full page. Use of the Burst Stop Command during other
burst length operations is illegal. The Burst Stop Command is defined by having RAS and CAS high with CS and WE low at the
rising edge of the clock. The data DQs go to a high impedance state after a delay which is equal to the CAS Latency in a burst
read cycle interrupted by Burst Stop. If a Burst Stop Command is issued during a full page burst write operation, then any
residual data from the burst write cycle will be ignored.

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W981216AH

Access Address

Burst Length

A8 A7 A6 A5 A4 A3 A2 A1 A0

BL = 2

A8 A7 A6 A5 A4 A3 A2 A1 A0

A8 A7 A6 A5 A4 A3 A2 A1 A0

BL = 4

A8 A7 A6 A5 A4 A3 A2 A1 A0

A8 A7 A6 A5 A4 A3 A2 A1 A0

A8 A7 A6 A5 A4 A3 A2 A1 A0

BL = 8

A8 A7 A6 A5 A4 A3 A2 A1 A0

A8 A7 A6 A5 A4 A3 A2 A1 A0

2M x 16 bit x 4 Banks SDRAM

Table 2 Address Sequence of Sequential Mode

DATA Access Address Burst Length
Data 0 n BL= 2 (disturb address is A0)
Data 1 n + 1 No address carry from A0 to A1
Data 2 n + 2 BL= 4 (disturb addresses are A0 and A1)
Data 3 n + 3 No address carry from A1 to A2
Data 4 n + 4
Data 5 n + 5 BL= 8 (disturb addresses are A0, A1 and A2)
Data 6 n + 6 No address carry from A2 to A3
Data 7 n + 7

. Addressing Sequence of Sequential Mode

A column access is performed by increasing the address from the column address which is input to the
device. The disturb address is varied by the Burst Length as shown in Table 2.

. Addressing Sequence of Interleave Mode

A column access is started in the input column address and is performed by inverting the address bit in the
sequence shown in Table 3.

Table 3 Address Sequence of Interleave Mode

DATA
Data 0
Data 1
Data 2
Data 3
Data 4
Data 5
Data 6
Data 7

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W981216AH

2M x 16 bit x 4 Banks SDRAM

Auto-Precharge Command

If A10 is set to high when the Read or Write Command is issued, then the auto-precharge function is entered. During auto­precharge, a Read Command will execute as normal with the exception that the active bank will begin to precharge automatically
before all burst read cycles have been completed. Regardless of burst length, it will begin a certain number of clocks prior to the
end of the scheduled burst cycle. The number of clocks is determined by CAS latency.
A Read or Write Command with auto-precharge can not be interrupted before the entire burst operation is completed. Therefore,
use of a Read, Write, or Precharge Command is prohibited during a read or write cycle with auto-precharge. Once the precharge
operation has started, the bank cannot be reactivated until the Precharge time (tRP) has been satisfied. Issue of Auto-Precharge
command is illegal if the burst is set to full page length. If A10 is high when a Write Command is issued, the Write with Auto­Precharge function is initiated. The SDRAM automatically enters the precharge operation one clock delay from the last burst
write cycle. This delay is referred to as Write tDPL. The bank undergoing auto-precharge can not be reactivated until tDPL and tRP are
satisfied. This is referred to as tDAL, Data-in to Active delay (tDAL = tDPL + tRP). When using the Auto-precharge Command, the
interval between the Bank Activate Command and the beginning of the internal precharge operation must satisfy tRAS(min).

Precharge Command

The Precharge Command is used to precharge or close a bank that has been activated. The Precharge Command is entered when
CS, RAS and WE are low and CAS is high at the rising edge of the clock. The Precharge Command can be used to precharge
each bank separately or all banks simultaneously. Three address bits, A10, A12, and A13, are used to define which bank(s) is to
be precharged when the command is issued. After the Precharge Command is issued, the precharged bank must be reactivated
before a new read or write access can be executed. The delay between the Precharge Command and the Activate Command must
be greater than or equal to the Precharge time (tRP).

Self Refresh Command

The Self Refresh Command is defined by having CS, RAS, CAS and CKE held low with WE high at the rising edge of the clock.
All banks must be idle prior to issuing the Self Refresh Command. Once the command is registered, CKE must be held low to
keep the device in Self Refresh mode. When the SDRAM has entered Self Refresh mode all of the external control signals, except
CKE, are disabled. The clock is internally disabled during Self Refresh Operation to save power. The device will exit Self
Refresh operation after CKE is returned high. A minimum delay time is required when the device exits Self Refresh Operation
and before the next command can be issued. This delay is equal to the RAS cycle time plus the Self Refresh exit time.

Power Down Mode

The Power Down mode is initiated by holding CKE low. All of the receiver circuits except CKE are gated off to reduce the
power. The Power Down mode does not perform any refresh operations, therefore the device can not remain in Power Down
mode longer than the Refresh period (tREF) of the device.

The Power Down mode is exited by bringing CKE high. When CKE goes high, a No Operation Command is required on the next
rising clock edge, depending on tCK. The input buffers need to be enabled with CKE held high for a period equal to tCES(min) +
tCK(min).

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W981216AH

2M x 16 bit x 4 Banks SDRAM

No Operation Command

The No Operation Command should be used in cases when the SDRAM is in a idle or a wait state to prevent the SDRAM from
registering any unwanted commands between operations. A No Operation Command is registered when CS is low with RAS,
CAS, and WE held high at the rising edge of the clock. A No Operation Command will not terminate a previous operation that is
still executing, such as a burst read or write cycle.

Deselect Command

The Deselect Command performs the same function as a No Operation Command. Deselect Command occurs when CS is brought
high, the RAS, CAS, and WE signals become don't cares.

Clock Suspend Mode

During normal access mode, CKE must be held high enabling the clock. When CKE is registered low while at least one of the
banks is active, Clock Suspend Mode is entered. The Clock Suspend mode deactivates the internal clock and suspends any
clocked operation that was currently being executed. There is a one clock delay between the registration of CKE low and the
time at which the SDRAM operation suspends. While in Clock Suspend mode, the SDRAM ignores any new commands that are
issued. The Clock Suspend mode is exited by bringing CKE high. There is a one clock cycle delay from when CKE returns high
to when Clock Suspend mode is exited.

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