Preliminary
GS8672T20/38AE-550/500/450/400
165-Bump BGA
Commercial Temp
Industrial Temp
Features
• 2.5 Clock Latency
• On-Chip ECC with virtually zero SER
• Simultaneous Read and Write SigmaDDR™ Interface
• Common I/O bus
• JEDEC-standard package
• Double Data Rate interface
• Byte Write capability
• Burst of 2 Read and Write
• On-Die Termination (ODT) on Data (D), Byte Write (BW),
and Clock (K, K) outputs
• 1.8 V +100/–100 mV core power supply
• 1.5 V HSTL Interface
• Pipelined read operation with self-timed Late Write
• Fully coherent read and write pipelines
• ZQ pin for programmable output drive strength
• IEEE 1149.1 JTAG-compliant Boundary Scan
• Pin-compatible with future 144Mb and 288Mb devices
• 165-bump, 15 mm x 17 mm, 1 mm bump pitch BGA package
• RoHS-compliant 165-bump BGA package available
72Mb SigmaDDR-II+
Burst of 2 ECCRAM
TM
Clocking and Addressing Schemes
550 MHz–400 MHz
1.8 V V
DD
1.5 V I/O
The GS8672T20/38AE SigmaDDR-II+ SRAMs are
synchronous devices. They employ two input register clock
inputs, K and K. K and K are independent single-ended clock
inputs, not differential inputs to a single differential clock input
buffer.
Because Common I/O SigmaDDR-II+ ECCRAMs always
transfer data in two packets, A0 is internally set to 0 for the
first read or write transfer, and automatically incremented by 1
for the next transfer. Because the LSB is tied off internally, the
address field of a SigmaDDR-II+ B2 RAM is always one
address pin less than the advertised index depth (e.g., the 4M x
18 has a 2M addressable index).
On-Chip Error Correction Code
GSI's ECCRAMs implement an ECC algorithm that detects
and corrects all single-bit memory errors, including those
induced by Soft Error Rate (SER) events such as cosmic rays,
alpha particles etc. The resulting SER of these devices is
anticipated to be <0.002 FITs/Mb — a 5-order-of-magnitude
improvement over comparable SRAMs with no On-Chip ECC,
which typically have an SER of 200 FITs/Mb or more. SER
quoted above is based on reading taken at sea level.
However, the On-Chip Error Correction (ECC) will be
disabled if a “Half Write” operation is initiated. See the
Byte
Write Contol
section for further information.
SigmaDDR™ Family Overview
The GS8672T20/38AE SigmaDDR-II+ ECCRAMs are built in
compliance with the SigmaDDR-II+ SRAM pinout standard
for Common I/O synchronous SRAMs. They are
75,497,472-bit (72Mb) SRAMs. The GS8672T20/38AE
SigmaDDR SRAMs are just one element in a family of low
power, low voltage HSTL I/O SRAMs designed to operate at
the speeds needed to implement economical high performance
networking systems.
Parameter Synopsis
-550
tKHKH
tKHQV
1.81 ns
0.45 ns
-500
2.0 ns
0.45 ns
-450
2.2 ns
0.45 ns
-400
2.5 ns
0.45 ns
Rev: 1.00 5/2010
1/28
© 2010, GSI Technology
Specifications cited are subject to change without notice. For latest documentation see http://www.gsitechnology.com.
Preliminary
GS8672T20/38AE-550/500/450/400
Pin Description Table
Symbol
SA
R/W
BW0–BW3
LD
K
K
TMS
TDI
TCK
TDO
V
REF
ZQ
DQ
Description
Synchronous Address Inputs
Synchronous Read/Write
Synchronous Byte Writes
Synchronous Load Pin
Input Clock
Input Clock
Test Mode Select
Test Data Input
Test Clock Input
Test Data Output
HSTL Input Reference Voltage
Output Impedance Matching Input
Data I/O
Disable DLL when low
Output Echo Clock
Output Echo Clock
Power Supply
Isolated Output Buffer Supply
Power Supply: Ground
Q Valid Output
On-Die Termination
No Connect
No Function
Type
Input
Input
Input
Input
Input
Input
Input
Input
Input
Output
Input
Input
Input/Output
Input
Output
Output
Supply
Supply
Supply
Output
Input
—
—
Comments
—
High: Read
Low: Write
Active Low
Active Low
Active High
Active Low
—
—
—
—
—
—
Three State
Active Low
—
—
1.8 V Nominal
1.5 V Nominal
—
—
—
—
—
Doff
CQ
CQ
V
DD
V
DDQ
V
SS
QVLD
ODT
NC
NF
Notes:
1. NC = Not Connected to die or any other pin
2. NF = No Function. There is an electrical connection to this input pin, but the signal has no function in the device. It can be left unconnected,
or tied to V
SS
or V
DDQ.
3. K, or K cannot be set to V
REF
voltage.
Rev: 1.00 5/2010
4/28
© 2010, GSI Technology
Specifications cited are subject to change without notice. For latest documentation see http://www.gsitechnology.com.
Preliminary
GS8672T20/38AE-550/500/450/400
Background
Common I/O SRAMs, from a system architecture point of view, are attractive in read dominated or block transfer applications.
Therefore, the SigmaDDR-II+ ECCRAM interface and truth table are optimized for burst reads and writes. Common I/O SRAMs
are unpopular in applications where alternating reads and writes are needed because bus turnaround delays can cut high speed
Common I/O SRAM data bandwidth in half.
Burst Operations
Read and write operations are burst operations. In every case where a read or write command is accepted by the ECCRAM, it will
respond by issuing or accepting two beats of data, executing a data transfer on subsequent rising edges of K and K, as illustrated in
the timing diagrams. It is not possible to stop a burst once it starts. Two beats of data are always transferred. This means that it is
possible to load new addresses every K clock cycle. Addresses can be loaded less often, if intervening deselect cycles are inserted.
Deselect Cycles
Chip Deselect commands are pipelined to the same degree as read commands. This means that if a deselect command is applied to
the ECCRAM on the next cycle after a read command captured by the ECCRAM, the device will complete the two beat read data
transfer and then execute the deselect command, returning the output drivers to High-Z. A high on the LD pin prevents the RAM
from loading read or write command inputs and puts the RAM into deselect mode as soon as it completes all outstanding burst
transfer operations.
SigmaDDR-II+ B2 ECCRAM Read Cycles
The SRAM executes pipelined reads. The status of the Address, LD and R/W pins are evaluated on the rising edge of K. The read
command (LD low and R/W high) is clocked into the SRAM by a rising edge of K.
SigmaDDR-II+ B2 ECCRAM Write Cycles
The status of the Address, LD and R/W pins are evaluated on the rising edge of K. The ECCRAM executes Late write data
transfers. Data in is due at the device inputs on the rising edge of K following the rising edge of K clock used to clock in the write
command (LD and R/W low) and the write address. To complete the remaining beat of the burst of two write transfer, the
ECCRAM captures data in on the next rising edge of K, for a total of two transfers per address load.
Rev: 1.00 5/2010
5/28
© 2010, GSI Technology
Specifications cited are subject to change without notice. For latest documentation see http://www.gsitechnology.com.
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