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IS41C16256-60T

256K x 16 (4-MBIT) DYNAMIC RAM WITH EDO PAGE MODE

Integrated Silicon Solution 

IS41C16256

IS41LV16256

ISSI ®

Functional Description

The IS41C16256 and IS41LV16256 is a CMOS DRAM

optimized for high-speed bandwidth, low power applica-

tions. During READ or WRITE cycles, each bit is uniquely

addressed through the 18 address bits. These are en-

tered nine bits (A0-A8) at a time. The row address is

latched by the Row Address Strobe (RAS). The column

address is latched by the Column Address Strobe (CAS).

RAS is used to latch the first nine bits and CAS is used the

latter nine bits.

The IS41C16256 and IS41LV16256 has two CAS con-

trols, LCAS and UCAS. The LCAS and UCAS inputs

internally generates a CAS signal functioning in an iden-

tical manner to the single CAS input on the other 256K x

16 DRAMs. The key difference is that each CAS controls

its corresponding I/O tristate logic (in conjunction with OE

and WE and RAS). LCAS controls I/O0 through I/O7 and

UCAS controls I/O8 through I/O15.

The IS41C16256 and IS41LV16256 CAS function is

determined by the first CAS (LCAS or UCAS) transitioning

LOW and the last transitioning back HIGH. The two CAS

controls give the IS41C16256 both BYTE READ and

BYTE WRITE cycle capabilities.

Memory Cycle

A memory cycle is initiated by bring RAS LOW and it is

terminated by returning both RAS and CAS HIGH. To

ensures proper device operation and data integrity any

memory cycle, once initiated, must not be ended or

aborted before the minimum tRAS time has expired. A new

cycle must not be initiated until the minimum precharge

time tRP, tCP has elapsed.

Read Cycle

A read cycle is initiated by the falling edge of CAS or OE,

whichever occurs last, while holding WE HIGH. The

column address must be held for a minimum time speci-

fied by tAR. Data Out becomes valid only when tRAC, tAA,

tCAC and tOEA are all satisfied. As a result, the access time

is dependent on the timing relationships between these

parameters.

Write Cycle

A write cycle is initiated by the falling edge of CAS and

WE, whichever occurs last. The input data must be valid

at or before the falling edge of CAS or WE, whichever

occurs last.

4

Refresh Cycle

To retain data, 512 refresh cycles are required in each

8 ms period. There are two ways to refresh the memory.

1. By clocking each of the 512 row addresses (A0 through

A8) with RAS at least once every 8 ms. Any read, write,

read-modify-write or RAS-only cycle refreshes the ad-

dressed row.

2. Using a CAS-before-RAS refresh cycle. CAS-before-

RAS refresh is activated by the falling edge of RAS,

while holding CAS LOW. In CAS-before-RAS refresh

cycle, an internal 9-bit counter provides the row ad-

dresses and the external address inputs are ignored.

CAS-before-RAS is a refresh-only mode and no data

access or device selection is allowed. Thus, the output

remains in the High-Z state during the cycle.

Extended Data Out Page Mode

EDO page mode operation permits all 512 columns within

a selected row to be randomly accessed at a high data

rate.

In EDO page mode read cycle, the data-out is held to the

next CAS cycle’s falling edge, instead of the rising edge.

For this reason, the valid data output time in EDO page

mode is extended compared with the fast page mode. In

the fast page mode, the valid data output time becomes

shorter as the CAS cycle time becomes shorter. There-

fore, in EDO page mode, the timing margin in read cycle

is larger than that of the fast page mode even if the CAS

cycle time becomes shorter.

In EDO page mode, due to the extended data function, the

CAS cycle time can be shorter than in the fast page mode

if the timing margin is the same.

The EDO page mode allows both read and write opera-

tions during one RAS cycle, but the performance is

equivalent to that of the fast page mode in that case.

Power-On

After application of the VCC supply, an initial pause of

200 µs is required followed by a minimum of eight initial-

ization cycles (any combination of cycles containing a

RAS signal).

During power-on, it is recommended that RAS track with

VCC or be held at a valid VIH to avoid current surges.

Integrated Silicon Solution, Inc. — 1-800-379-4774

Rev. J

06/29/00

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