Samsung K4S643232C-TL55, K4S643232C-TL10, K4S643232C-TC80, K4S643232C-TC70, K4S643232C-TC60 Datasheet

K4S643232C CMOS SDRAM

2M x 32 SDRAM

512K x 32bit x 4 Banks

Synchronous DRAM

LVTTL

Revision 1.1

November 1999

Samsung Electronics reserves the right to change products or specification without notice.

- 1 -

REV. 1.1 Nov. '99

K4S643232C CMOS SDRAM

Revision History

Revision 1.1 (November 17th, 1999)

• Corrected typo in ordering information on page 3

Revision 1.0 (October, 1999)

• Changed part number from KM432S2030CT-G/F to K4S643232C-TC/TL according to re-organized code system

- 2 -

REV. 1.1 Nov. '99

K4S643232C CMOS SDRAM

512K x 32Bit x 4 Banks Synchronous DRAM

GENERAL DESCRIPTIONFEATURES

• 3.3V power supply

• LVTTL compatible with multiplexed address

• Four banks operation

• MRS cycle with address key programs

-. CAS latency (2 & 3)

-. Burst length (1, 2, 4, 8 & Full page)

-. Burst type (Sequential & Interleave)

• All inputs are sampled at the positive going edge of the system
clock

• Burst read single-bit write operation

• DQM for masking

• Auto & self refresh

• 15.6us refresh duty cycle

The K4S643232C is 67,108,864 bits synchronous high data
rate Dynamic RAM organized as 4 x 524,288 words by 32 bits,
fabricated with SAMSUNG′s high performance CMOS technol­ogy. Synchronous design allows precise cycle control with the
use of system clock. I/O transactions are possible on every
clock cycle. Range of operating frequencies, programmable
burst length and programmable latencies allow the same device
to be useful for a variety of high bandwidth, high performance
memory system applications.

ORDERING INFORMATION

Part NO. Max Freq. Interface Package

K4S643232C-TC/L55 183MHz
K4S643232C-TC/L60 166MHz
K4S643232C-TC/L70 143MHz
K4S643232C-TC/L80 125MHz
K4S643232C-TC/L10 100MHz

LVTTL

86

TSOP(II)

FUNCTIONAL BLOCK DIAGRAM

Bank Select

Refresh Counter

Row Buffer

Address Register

CLK

ADD

LRAS

LCBR

LCKE

LRAS LCBR LWE LDQM

Data Input Register

Row Decoder Col. Buffer

LCAS LWCBR

512K x 32
512K x 32
512K x 32
512K x 32

Column Decoder

Latency & Burst Length

Programming Register

LWE

LDQM

Sense AMP

Output BufferI/O Control

DQi

Timing Register

CLK CKE CS RAS CAS WE DQM

- 3 -

Samsung Electronics reserves the right to

*

change products or specification without
notice.

REV. 1.1 Nov. '99

K4S643232C CMOS SDRAM

PIN CONFIGURATION (Top view)

VDD

DQ0

VDDQ

DQ1
DQ2

VSSQ

DQ3
DQ4

VDDQ

DQ5
DQ6

VSSQ

DQ7

N.C
VDD

DQM0

WE
CAS
RAS

CS

N.C
BA0
BA1

A10/AP

A0
A1
A2

DQM2

VDD

N.C

DQ16

VSSQ
DQ17
DQ18

VDDQ
DQ19
DQ20

VSSQ
DQ21
DQ22

VDDQ

DQ23

VDD

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
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43

86
85
84
83
82
81
80
79
78
77
76
75
74
73
72
71
70
69
68
67
66
65
64
63
62
61
60
59
58
57
56
55
54
53
52
51
50
49
48
47
46
45
44

VSS
DQ15
VSSQ
DQ14
DQ13
VDDQ
DQ12
DQ11
VSSQ
DQ10
DQ9
VDDQ
DQ8
N.C
VSS
DQM1
N.C
N.C
CLK
CKE
A9
A8
A7
A6
A5
A4
A3
DQM3
VSS
N.C
DQ31
VDDQ
DQ30
DQ29
VSSQ
DQ28
DQ27
VDDQ
DQ26
DQ25
VSSQ
DQ24
VSS

86Pin TSOP (II)

(400mil x 875mil)

(0.5 mm Pin pitch)

- 4 -

REV. 1.1 Nov. '99

K4S643232C CMOS SDRAM

PIN FUNCTION DESCRIPTION

Pin Name Input Function

CLK System clock Active on the positive going edge to sample all inputs.
CS Chip select

CKE Clock enable

A0 ~ A10 Address

BA0,1 Bank select address

RAS Row address strobe

CAS Column address strobe

WE Write enable

DQM0 ~ 3 Data input/output mask

DQ0 ~ 31 Data input/output Data inputs/outputs are multiplexed on the same pins.
VDD/VSS Power supply/ground Power and ground for the input buffers and the core logic.

VDDQ/VSSQ Data output power/ground

NC No Connection This pin is recommended to be left No connection on the device.

Disables or enables device operation by masking or enabling all inputs except
CLK, CKE and DQM.

Masks system clock to freeze operation from the next clock cycle.
CKE should be enabled at least one cycle prior to new command.
Disables input buffers for power down mode.

Row/column addresses are multiplexed on the same pins.
Row address : RA0 ~ RA10, Column address : CA0 ~ CA7

Selects bank to be activated during row address latch time.
Selects bank for read/write during column address latch time.

Latches row addresses on the positive going edge of the CLK with RAS low.
Enables row access & precharge.

Latches column addresses on the positive going edge of the CLK with CAS low.
Enables column access.

Enables write operation and row precharge.
Latches data in starting from CAS, WE active.

Makes data output Hi-Z, tSHZ after the clock and masks the output.
Blocks data input when DQM active.

Isolated power supply and ground for the output buffers to provide improved noise
immunity.

ABSOLUTE MAXIMUM RATINGS

Parameter Symbol Value Unit

Voltage on any pin relative to Vss VIN, VOUT -1.0 ~ 4.6 V
Voltage on VDD supply relative to Vss VDD, VDDQ -1.0 ~ 4.6 V
Storage temperature TSTG -55 ~ +150 °C
Power dissipation PD 1 W
Short circuit current IOS 50 mA

Note :

Permanent device damage may occur if "ABSOLUTE MAXIMUM RATINGS" are exceeded.
Functional operation should be restricted to recommended operating condition.
Exposure to higher than recommended voltage for extended periods of time could affect device reliability.

CAPACITANCE (VDD = 3.3V, TA = 23°C, f = 1MHz, VREF = 1.4V ± 200 mV)

Pin Symbol Min Max Unit

Clock CCLK 2.5 4 pF
RAS, CAS, WE, CS, CKE, DQM CIN 2.5 4.5 pF
Address CADD 2.5 4.5 pF
DQ0 ~ DQ31 COUT 4.0 6.5 pF

- 5 -

REV. 1.1 Nov. '99

K4S643232C CMOS SDRAM

DC OPERATING CONDITIONS

Recommended operating conditions (Voltage referenced to VSS = 0V, TA = 0 to 70°C)

Parameter Symbol Min Typ Max Unit Note

Supply voltage VDD, VDDQ 3.0 3.3 3.6 V 4
Input logic high voltage VIH 2.0 3.0 VDDQ+0.3 V 1
Input logic low voltage VIL -0.3 0 0.8 V 2
Output logic high voltage VOH 2.4 - - V IOH = -2mA
Output logic low voltage VOL - - 0.4 V IOL = 2mA
Input leakage current ILI -10 - 10 uA 3

Notes :

1. VIH (max) = 5.6V AC.The overshoot voltage duration is ≤ 3ns.

2. VIL (min) = -2.0V AC. The undershoot voltage duration is ≤ 3ns.

3. Any input 0V ≤ VIN ≤ VDDQ,
Input leakage currents include Hi-Z output leakage for all bi-directional buffers with Tri-State outputs.

4. The VDD condition of K4S643232C-55/60 is 3.135V~3.6V.

DC CHARACTERISTICS

(Recommended operating condition unless otherwise noted, TA = 0 to 70°C)

Parameter Symbol Test Condition

Operating current
(One bank active)

Precharge standby current
in power-down mode

Precharge standby current
in non power-down mode

Active standby current in
power-down mode

Active standby current in
non power-down mode
(One bank active)

Operating current
(Burst mode)

Refresh current ICC5 tRC ≥ tRC(min)

Self refresh current ICC6 CKE ≤ 0.2V

Notes :

1. Unless otherwise notes, Input level is CMOS(VIH/VIL=VDDQ/VSSQ) in LVTTL.

2. Measured with outputs open.

3. Refresh period is 64ms.

4. K4S643232C-TC**

5. K4S643232C-TL**

ICC2P CKE ≤ VIL(max), tCC = 15ns 2

ICC2PS CKE & CLK ≤ VIL(max), tCC = ∞ 2

ICC2N

ICC2NS

ICC3P CKE ≤ VIL(max), tCC = 15ns 3

ICC3PS CKE & CLK ≤ VIL(max), tCC = ∞ 3

ICC3N

ICC3NS

Burst length = 1

ICC1

tRC ≥ tRC(min)
Io = 0 mA

CKE ≥ VIH(min), CS ≥ VIH(min), tCC = 15ns
Input signals are changed one time during 30ns

CKE ≥ VIH(min), CLK ≤ VIL(max), tCC = ∞
Input signals are stable

CKE ≥ VIH(min), CS ≥ VIH(min), tCC = 15ns
Input signals are changed one time during 30ns

CKE ≥ VIH(min), CLK ≤ VIL(max), tCC = ∞
Input signals are stable

Io = 0 mA
Page burst

ICC4

2 Banks activated

CAS

Latency

-55 -60 -70 -80 -10

3 140 140 130 130 115
2 - - - 130 115

3 220 200 180 150 130
2 - - - 130 110

3 200 200 180 160 150
2 - - - 160 150

Version

20 mA

10 mA

30 mA

20 mA

2 mA 4

450 uA 5

Unit Note

mA 2

mA

mA

mA 2

mA 3

- 6 -

REV. 1.1 Nov. '99

K4S643232C CMOS SDRAM

AC OPERATING TEST CONDITIONS (VDD = 3.3V ± 0.3V, TA = 0 to 70°C)

Parameter Value Unit

AC input levels (Vih/Vil) 2.4/0.4 V
Input timing measurement reference level 1.4 V
Input rise and fall time tr/tf = 1/1 ns
Output timing measurement reference level 1.4 V
Output load condition See Fig. 2

3.3V

1200Ω

Output

870Ω

Note :

1. The DC/AC Test Output Load of K4S643232C-55/60/70 is 30pF.

2. The VDD condition of K4S643232C-55/60 is 3.135V~3.6V.

50pF

VOH (DC) = 2.4V, IOH = -2mA
VOL (DC) = 0.4V, IOL = 2mA

*1

Output

Z0 = 50Ω

(Fig. 2) AC output load circuit (Fig. 1) DC output load circuit

Vtt = 1.4V

50Ω

*1

50pF

OPERATING AC PARAMETER

(AC operating conditions unless otherwise noted)

Parameter Symbol

CAS Latency CL 3 2 3 2 3 2 3 2 3 2 CLK
CLK cycle time tCC(min) 5.5 - 6 - 7 - 8 10 10 12 ns
Row active to row active delay tRRD(min) 2 CLK 1
RAS to CAS delay tRCD(min) 3 - 3 - 3 - 3 2 2 2 CLK 1
Row precharge time tRP(min) 3 - 3 - 3 - 3 2 2 2 CLK 1

Row active time
Row cycle time

Row cycle time in Auto refresh tRFC(min) 12 - 12 - 10 - 9 7 7 6 CLK 1,6
Last data in to row precharge tRDL(min) 2 CLK 2, 5
Last data in to new col.address delay tCDL(min) 1 CLK 2
Last data in to burst stop tBDL(min) 1 CLK 2
Col. address to col. address delay tCCD(min) 1 CLK
Mode Register Set cycle time tMRS(min) 2 CLK

Number of valid output data

CAS Latency=3 2
CAS Latency=2 1

tRAS(min) 7 - 7 - 7 - 6 5 5 4 CLK 1

tRAS(max) 100 us

tRC(min) 10 - 10 - 10 - 9 7 7 6 CLK 1

-55 -60 -70 -80 -10

Version

Unit Note

ea 4

Note :

1. The minimum number of clock cycles is determined by dividing the minimum time required with clock cycle time and then
rounding off to the next higher integer. Refer to the following ns-unit based AC table.

- 7 -

REV. 1.1 Nov. '99

K4S643232C CMOS SDRAM

Parameter Symbol

CLK cycle time tCC(min) 5.5 6 7 8 10 ns
Row active to row active delay tRRD(min) 11 12 14 16 20 ns
RAS to CAS delay tRCD(min) 16.5 18 21 20 20 ns
Row precharge time tRP(min) 16.5 18 21 20 20 ns

Row active time
Row cycle time tRC(min) 55 60 70 70 70 ns

Row cycle time in Auto refresh tRFC(min) 66 72 70 70 70 ns

2. Minimum delay is required to complete write.

3. All parts allow every cycle column address change.

4. In case of row precharge interrupt, auto precharge and read burst stop.

5. For -55/60/70/80/10, tRDL=1CLK product can be supported within restricted amounts and it will be distinguished by bucket
code "NV". From the next generation, tRDL will be only 2CLK for every clock frequency.

6. A new command should be issued after self refersh exit followed by tRFC.

tRAS(min) 38.5 42 49 48 48 ns
tRAS(max) 100 us

-55 -60 -70 -80 -10

Version

Unit

AC CHARACTERISTICS (AC operating conditions unless otherwise noted)

Parameter Symbol

CLK cycle time

CLK to valid
output delay

Output data tOH 2 - 2.5 - 2.5 - 2.5 - 2.5 - ns 2

CLK high pulse width

CLK low pulse width

Input setup time

Input hold time tSH 1 - 1 - 1 - 1 - 1 - ns 3
CLK to output in Low-Z tSLZ 1 - 1 - 1 - 1 - 1 - ns 2

CLK to output
in Hi-Z

CAS Latency=3
CAS Latency=2 - - - 10 12
CAS Latency=3
CAS Latency=2 - - - - - - - 6 - 8

CAS Latency=3
CAS Latency=2 - ­CAS Latency=3
CAS Latency=2 - ­CAS Latency=3
CAS Latency=2 - -

CAS Latency=3
CAS Latency=2 - - - - - - - 6 - 8

tCC

tSAC

tCH

tCL

tSS

tSHZ

-55 -60 -70 -80 -10

Min Max Min Max Min Max Min Max Min Max

5.5
1000

- 5 - 5.5 - 5.5 - 6 - 6

2 - 2.5

2 - 2.5

1.5 - 1.5

- 5 - 5.5 - 5.5 - 6 - 6

6

1000

-

-

-

7

1000

- 3 - 3 - 3.5 - ns 3

- 3 - 3 - 3.5 - ns 3

1.75

-

-

8

- 2 - 2.5 - ns 3

1000

10

1000 ns 1

Unit Note

ns 1, 2

ns

Note :

1. Parameters depend on programmed CAS latency.

2. If clock rising time is longer than 1ns, (tr/2-0.5)ns should be added to the parameter.

3. Assumed input rise and fall time (tr & tf)=1ns.
If tr & tf is longer than 1ns, transient time compensation should be considered,
i.e., [(tr + tf)/2-1]ns should be added to the parameter.

- 8 -

REV. 1.1 Nov. '99

K4S643232C CMOS SDRAM

SIMPLIFIED TRUTH TABLE

Command CKEn-1 CKEn CS RAS CAS WE DQM BA0,1 A10/AP

Register Mode register set H X L L L L X OP code 1,2

Auto refresh

Refresh

Bank active & row addr. H X L L H H X V Row address
Read &

column address

Write &
column address

Burst Stop H X L H H L X X 6

Precharge

Clock suspend or
active power down

Precharge power down mode

DQM H V X 7

No operation command H X

(V=Valid, X=Don′t care, H=Logic high, L=Logic low)

Notes :

1. OP Code : Operand code
A0 ~ A10 & BA0 ~ BA1 : Program keys. (@ MRS)

2. MRS can be issued only at all banks precharge state.
A new command can be issued after 2 CLK cycles of MRS.

3. Auto refresh functions are as same as CBR refresh of DRAM.
The automatical precharge without row precharge command is meant by "Auto".
Auto/self refresh can be issued only at all banks precharge state.

4. BA0 ~ BA1 : Bank select addresses.
If both BA0 and BA1 are "Low" at read, write, row active and precharge, bank A is selected.
If both BA0 is "Low" and BA1 is "High" at read, write, row active and precharge, bank B is selected.
If both BA0 is "High" and BA1 is "Low" at read, write, row active and precharge, bank C is selected.
If both BA0 and BA1 are "High" at read, write, row active and precharge, bank D is selected.
If A10/AP is "High" at row precharge, BA0 and BA1 is ignored and all banks are selected.

5. During burst read or write with auto precharge, new read/write command can not be issued.
Another bank read/write command can be issued after the end of burst.
New row active of the associated bank can be issued at tRP after the end of burst.

6. Burst stop command is valid at every burst length.

7. DQM sampled at positive going edge of a CLK and masks the data-in at the very CLK (Write DQM latency is 0),
but makes Hi-Z state the data-out of 2 CLK cycles after. (Read DQM latency is 2)

Self
refresh

Auto precharge disable
Auto precharge enable H 4,5
Auto precharge disable
Auto precharge enable H 4,5

Bank selection
All banks X H

Entry L 3

Exit L H

Entry H L

Exit L H X X X X X

Entry H L

Exit L H

H

H X L H L H X V

H X L H L L X V

H X L L H L X

H

L L L H X X

L H H H

H X X X 3

H X X X

L V V V

H X X X

L H H H

H X X X

L V V V

X

H X X X

L H H H

X X

L

L

V L

X

X

X

X

X

X X

,

A9 ~ A0

Column
address

(A0 ~ A7)

Column
address

(A0 ~ A7)

X

Note

3

3

4

4

- 9 -

REV. 1.1 Nov. '99

K4S643232C CMOS SDRAM

MODE REGISTER FIELD TABLE TO PROGRAM MODES

Register Programmed with MRS

Address
Function

A8 A7 A6 A5 A4 A3 A2 A1 A0 BT = 0

A9

BA0 ~ BA1

RFU

Test Mode

0
0
1
1

0
1

0
1
0
1

Write Burst Length

A10/AP

RFU

Type

Mode Register Set

Reserved
Reserved
Reserved

Length

Burst

Single Bit

A9

W.B.L

0
0
0
0
1
1
1
1

A8 A7

TM

CAS Latency

0

0

0

1

1

0

1

1

0

0

0

1

1

0

1

1

A6 A5 A4 A3 A2 A1 A0

CAS Latency BT Burst Length

Latency
Reserved
Reserved

2

3
Reserved
Reserved
Reserved
Reserved

Burst Type

0

Sequential

1

Interleave

Type

0
0
0
0
1
1
1
1

Burst Length

0

0

0

1

1

0

1

1
0
0
1
1

Full Page Length : x32 (256)

Reserved

0

Reserved

1

Reserved

0

Full Page

1

POWER UP SEQUENCE

SDRAMs must be powered up and initialized in a predefined manner to prevent undefined operations.

1. Apply power and start clock. Must maintain CKE= "H", DQM= "H" and the other pins are NOP condition at the inputs.

2. Maintain stable power, stable clock and NOP input condition for a minimum of 200us.

3. Issue precharge commands for all banks of the devices.

4. Issue 2 or more auto-refresh commands.

5. Issue a mode register set command to initialize the mode register.
cf.) Sequence of 4 & 5 is regardless of the order.

1
2
4
8

BT = 1

1
2
4

8
Reserved
Reserved
Reserved
Reserved

The device is now ready for normal operation.

Note : 1. If A9 is high during MRS cycle, "Burst Read Single Bit Write" function will be enabled.

2. RFU (Reserved for future use) should stay "0" during MRS cycle.

- 10

REV. 1.1 Nov. '99

K4S643232C CMOS SDRAM

BURST SEQUENCE (BURST LENGTH = 4)

Initial Address

A1 A0

0
0
1
1

0
1
0
1

0
1
2
3

BURST SEQUENCE (BURST LENGTH = 8)

Initial Address

A1 A0A2

0
0
0
0
1
1
1
1

0
0
1
1
0
0
1
1

0
1
0
1
0
1
0
1

0

1

1

2

2

3

3

4

4

5

5

6

6

7

7

0

Sequential Interleave

1
2
3
0

Sequential Interleave

2

3

3

4

4

5

5

6

6

7

7

0

0

1

1

2

2
3
0
1

4

5

5

6

6

7

7

0

0

1

1

2

2

3

3

4

3
0
1
2

6

7

7

0

0

1

1

2

2

3

3

4

4

5

5

6

0
1
2
3

0
1
2
3
4
5
6
7

2

1

3

0

0

3

1

2

6

5

7

4

4

7

5

6

1
0
3
2

3
2
1
0
7
6
5
4

2
3
0
1

4

5

5

4

6

7

7

6

0

1

1

0

2

3

3

2

3
2
1
0

6

7

7

6

4

5

5

4

2

3

3

2

0

1

1

0

- 11

REV. 1.1 Nov. '99

K4S643232C CMOS SDRAM

DEVICE OPERATIONS

CLOCK (CLK)

The clock input is used as the reference for all SDRAM opera­tions. All operations are synchronized to the positive going edge
of the clock. The clock transitions must be monotonic between
VIL and VIH. During operation with CKE high all inputs are
assumed to be in a valid state (low or high) for the duration of
set-up and hold time around positive edge of the clock in order
to function well Q perform and ICC specifications.

CLOCK ENABLE (CKE)

The clock enable(CKE) gates the clock onto SDRAM. If CKE
goes low synchronously with clock (set-up and hold time are the­same as other inputs), the internal clock is suspended from the
next clock cycle and the state of output and burst address is fro­zen as long as the CKE remains low. All other inputs are ignored
from the next clock cycle after CKE goes low. When all banks
are in the idle state and CKE goes low synchronously with clock,
the SDRAM enters the power down mode from the next clock
cycle. The SDRAM remains in the power down mode ignoring
the other inputs as long as CKE remains low. The power down
exit is synchronous as the internal clock is suspended. When
CKE goes high at least "1CLK + tSS" before the high going edge
of the clock, then the SDRAM becomes active from the same
clock edge accepting all the input commands.

NOP and DEVICE DESELECT

When RAS, CAS and WE are high, the SDRAM performs no
operation (NOP). NOP does not initiate any new operation, but
is needed to complete operations which require more than sin­gle clock cycle like bank activate, burst read, auto refresh, etc.
The device deselect is also a NOP and is entered by asserting
CS high. CS high disables the command decoder so that RAS,
CAS, WE and all the address inputs are ignored.

POWER-UP

SDRAMs must be powered up and initialized in a pre­defined manner to prevent undefined operations.

1. Apply power and start clock. Must maintain CKE= "H", DQM=
"H" and the other pins are NOP condition at the inputs.

2. Maintain stable power, stable clock and NOP input condition
for a minimum of 200us.

3. Issue precharge commands for both banks of the devices.

4. Issue 2 or more auto-refresh commands.

5. Issue a mode register set command to initialize the mode reg­ ister.
cf.) Sequence of 4 & 5 is regardless of the order.

BANK ADDRESSES (BA0 ~ BA1)

This SDRAM is organized as four independent banks of 524,288
words x 32 bits memory arrays. The BA0 ~ BA1 inputs are
latched at the time of assertion of RAS and CAS to select the
bank to be used for the operation. The bank addresses BA0 ~
BA1 are latched at bank active, read, write, mode register set
and precharge operations.

ADDRESS INPUTS (A0 ~ A10)

The 19 address bits are required to decode the 524,288 word
locations are multiplexed into 11 address input pins (A0 ~ A10).
The 11 bit row addresses are latched along with RAS and BA0 ~
BA1 during bank activate command. The 8 bit column addresses
are latched along with CAS, WE and BA0 ~ BA1 during read or
write command.

The device is now ready for normal operation.

- 12

REV. 1.1 Nov. '99

K4S643232C CMOS SDRAM

DEVICE OPERATIONS (Continued)

MODE REGISTER SET (MRS)

The mode register stores the data for controlling the various
operating modes of SDRAM. It programs the CAS latency, burst
type, burst length, test mode and various vendor specific options
to make SDRAM useful for variety of different applications. The
default value of the mode register is not defined, therefore the
mode register must be written after power up to operate the
SDRAM. The mode register is written by asserting low on CS,
RAS, CAS and WE (The SDRAM should be in active mode with
CKE already high prior to writing the mode register). The state of
address pins A0 ~ A10 and BA0 ~ BA1 in the same cycle as CS,
RAS, CAS and WE going low is the data written in the mode
register. Two clock cycles is required to complete the write in the
mode register. The mode register contents can be changed
using the same command and clock cycle requirements during
operation as long as all banks are in the idle state. The mode
register is divided into various fields depending on the fields of
functions. The burst length field uses A0 ~ A2, burst type uses
A3, CAS latency (read latency from column address) use A4 ~
A6, vendor specific options or test mode use A7 ~ A8, A10/AP
and BA0 ~ BA1. The write burst length is programmed using A9.
A7 ~ A8, A10/AP and BA0 ~ BA1 must be set to low for normal
SDRAM operation. Refer to the table for specific codes for vari­ous burst length, burst type and CAS latencies.

BANK ACTIVATE

The bank activate command is used to select a random row in
an idle bank. By asserting low on RAS and CS with desired row
and bank address, a row access is initiated. The read or write
operation can occur after a time delay of tRCD(min) from the time
of bank activation. tRCD is an internal timing parameter of
SDRAM, therefore it is dependent on operating clock frequency.
The minimum number of clock cycles required between bank
activate and read or write command should be calculated by
dividing tRCD(min) with cycle time of the clock and then rounding
off the result to the next higher integer. The SDRAM has four
internal banks in the same chip and shares part of the internal
circuitry to reduce chip area, therefore it restricts the activation
of four banks simultaneously. Also the noise generated during
sensing of each bank of SDRAM is high, requiring some time for
power supplies to recover before another bank can be sensed
reliably. tRRD(min) specifies the minimum time required between
activating different bank. The number of clock cycles required
between different bank activation must be calculated similar to
tRCD specification. The minimum time required for the bank to be

active to initiate sensing and restoring the complete row of
dynamic cells is determined by tRAS(min). Every SDRAM bank
activate command must satisfy tRAS(min) specification before a
precharge command to that active bank can be asserted. The
maximum time any bank can be in the active state is determined
by tRAS(max). The number of cycles for both tRAS(min) and
tRAS(max) can be calculated similar to tRCD specification.

BURST READ

The burst read command is used to access burst of data on con­secutive clock cycles from an active row in an active bank. The
burst read command is issued by asserting low on CS and CAS
with WE being high on the positive edge of the clock. The bank
must be active for at least tRCD(min) before the burst read com­mand is issued. The first output appears in CAS latency number
of clock cycles after the issue of burst read command. The burst
length, burst sequence and latency from the burst read com­mand is determined by the mode register which is already pro­grammed. The burst read can be initiated on any column
address of the active row. The address wraps around if the initial
address does not start from a boundary such that number of out­puts from each I/O are equal to the burst length programmed in
the mode register. The output goes into high-impedance at the
end of the burst, unless a new burst read was initiated to keep
the data output gapless. The burst read can be terminated by
issuing another burst read or burst write in the same bank or the
other active bank or a precharge command to the same bank.
The burst stop command is valid at every page burst length.

BURST WRITE

The burst write command is similar to burst read command and
is used to write data into the SDRAM on consecutive clock
cycles in adjacent addresses depending on burst length and
burst sequence. By asserting low on CS, CAS and WE with valid
column address, a write burst is initiated. The data inputs are
provided for the initial address in the same clock cycle as the
burst write command. The input buffer is deselected at the end
of the burst length, even though the internal writing can be com­pleted yet. The writing can be completed by issuing a burst read
and DQM for blocking data inputs or burst write in the same or
another active bank. The burst stop command is valid at every
burst length. The write burst can also be terminated by using
DQM for blocking data and procreating the bank tRDL after the
last data input to be written into the active row. See DQM
OPERATION also.

- 13

REV. 1.1 Nov. '99