Example x18 RAM Write Sequence using Byte Write Enables

Data In Sample Time

BW0

BW1

D0–D8

D9–D17

Beat 1

0

1

Data In

Don’t Care

Beat 2

1

0

Don’t Care

Data In

Beat 3

0

0

Data In

Data In

Beat 4

1

0

Don’t Care

Data In

Resulting Write Operation

Byte 1

D0–D8

Byte 2

D9–D17

Byte 1

D0–D8

Byte 2

D9–D17

Byte 1

D0–D8

Byte 2

D9–D17

Byte 1

D0–D8

Byte 2

D9–D17

Written

Unchanged

Unchanged

Written

Written

Written

Unchanged

Written

Beat 1

Beat 2

Beat 3

Beat 4

GS8342DT07/10/19/37BD-450/400/350/333/300

Specifications cited are subject to change without notice. For latest documentation see http://www.gsitechnology.com.

Rev: 1.01a 8/2017

8/29

© 2011, GSI Technology

FLXDrive-II Output Driver Impedance Control

HSTL I/O SigmaQuad-II+ SRAMs are supplied with programmable impedance output drivers. The ZQ pin must be connected to

5X the value of the desired RAM output impedance. The allowable range of RQ to guarantee impedance matching continuously is

between 175

 and 350. Periodic readjustment of the output driver impedance is necessary as the impedance is affected by drifts

in supply voltage and temperature. The SRAM’s output impedance circuitry compensates for drifts in supply voltage and

temperature. A clock cycle counter periodically triggers an impedance evaluation, resets and counts again. Each impedance

evaluation may move the output driver impedance level one step at a time towards the optimum level. The output driver is

implemented with discrete binary weighted impedance steps.

Input Termination Impedance Control

These SigmaQuad-II+ SRAMs are supplied with programmable input termination on Data (D), Byte Write (BW), and Clock (K,K)

input receivers. The input termination is always enabled, and the impedance is programmed via the same RQ resistor (connected

is tied Low, input termination is "strong" (i.e., low impedance), and is nominally equal to RQ*0.3 Thevenin-equivalent when RQ is

between 175Ω and 350Ω. When the ODT pin is tied High (or left floating—the pin has a small pull-up resistor), input termination

is "weak" (i.e., high impedance), and is nominally equal to RQ*0.6 Thevenin-equivalent when RQ is between 175Ω and 250Ω.

Periodic readjustment of the termination impedance occurs to compensate for drifts in supply voltage and temperature, in the same

manner as for driver impedance (see above).

Note:

D, BW, K, K inputs should always be driven High or Low; they should never be tri-stated (i.e., in a High-Z state). If the inputs are

the receiver to enter a meta-stable state, resulting in the receiver consuming more power than it normally would. This could result

in the device’s operating currents being higher.