Samsung DCB-P850Z, Service Manual

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Circuit Operating Descriptions
13-16 Samsung Electronics
2) Description
The 512-Mbit Double-Data-Rate SDRAM is a high-speed CMOS,
dynamic random-access memory containing 536,870,912 bits. It is internally configured as a quad-bankDRAM.
The 512-Mbit Double-Data-Rate SDRAM uses a double-data-rate architecture to achieve high-speed operation.
The double data rate architecture is essentially a 2n prefetch architecture with aninterface designed to
transfer two data words per clock cycle at the I/O pins.
A singleread or write access for the 512-Mbit Double-Data-Rate SDRAM effectively consists
of a single 2n-bit wide, one clock cycle data transfer at the internal DRAM core and two corresponding n-bit wide,
one-half-clock-cycle data transfers at the I/O pins.
A bidirectional data strobe (DQS) is transmitted externally, along with data,
for use indata capture at the receiver.
DQS is a strobe transmitted by the DDR SDRAM during Reads and by the memory controller during Writes.
DQS is edge-aligned with data for Reads and center-aligned with data for Writes.
The 512-Mbit Double-Data-Rate SDRAM operates from a differential clock
(CK and CK; the crossing of CK going HIGH and CK going LOW is referred to as the positive edge of CK).
Commands (address and control signals) are registered at every positive edge of CK.
Input data is registered on both edges of DQS, and output datais referenced to both edges of DQS,
as well as to both edges of CK.
Read and write accesses to the DDR SDRAM are burst oriented; accesses start at a selected location and continue
for a programmed number of locations in a programmed sequence.
Accesses begin with the registration of an Active command,
which is then followed by a Read or Write command.
The address bits registered coincident with the Active command are used to
select the bank and row to be accessed.
The address bits registered coincident with the Read or Write command are used to select the bank
and the starting column location for the burst access.
The DDR SDRAM provides for programmable Read or Write burst lengths of 2, 4 or 8 locations.
An Auto Precharge function may be enabled to provide a self-timed row
precharge that is initiated at the end of the burst access.
As with standard SDRAMs, the pipelined, multibank architecture of DDR SDRAMs allows for concurrent
operation, thereby providing high effective bandwidth by hiding row precharge and activation time.
An auto refresh mode is provided along with a power-saving power-down mode.
All inputs are compatible with the JEDEC Standard for SSTL_2. All outputs are SSTL_2, Class II compatible.