GS8182Q18D Datasheet, PDF (10/28 Pages) GSI Technology – 18Mb Burst of 2 SigmaQuad-II SRAM

Preliminary
GS8182Q18D-200/167/133
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
V_SS via an external resistor, RQ, to allow the SRAM to monitor and adjust its output driver impedance. The value of RQ must be
5X the value of the intended line impedance driven by the SRAM. The allowable range of RQ to guarantee impedance matching
with a vendor-specified tolerance is between 150Ω and 300Ω. 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 every 1024 cycles. 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.
Burst of 2 Coherency and Pass Through Functions
Because the Burst of 2 read and write commands are loaded at the same time, there may be some confusion over what constitutes
“coherent” operation. Normally, one would expect a RAM to produce the just-written data when it is read immediately after a
write. This is true of the Burst of 2 except in one case, as is illustrated in the following diagram. If the user holds the same address
value in a given K clock cycle, loading the same address as a read address and then as a matching write address, the Burst of 2 will
read or “Pass-thru” the latest data input, rather than the data from the previously completed write operation.
Dwg Rev. G
Read
K
Burst of 2 Coherency and Pass Through Functions
Write
Read
Write
Read
Write
Read
Write
/K
A
B
C
D
E
F
G
H
I
Address
OO
OI
OI
OO
OO
OO
OI
IO
OO
/R
/W
/BWx
DB0
DB1
DD0
DD1
DF0
DF1
DH0
DH1
DI0
D
5
6
8
2
7
1
9
3
4
C
COHERENT
PASS-THRU
/C
QA0
QA1
QC0
QC1
QE0
QE1
Q
?
?
5
6
7
1
Rev: 1.02 11/2004
10/28
Specifications cited are subject to change without notice. For latest documentation see http://www.gsitechnology.com.
© 2003, GSI Technology