Micron 2933 - Инструкция по эксплуатации - Страница 14

Registering Clock Driver Operation

Registered DDR4 SDRAM modules use a registering clock driver device consisting of a
register and a phase-lock loop (PLL). The device complies with the JEDEC DDR4 RCD
specification.

To reduce the electrical load on the host memory controller's command, address, and
control bus, Micron's RDIMMs utilize a DDR4 registering clock driver (RCD). The RCD
presents a single load to the controller while redriving signals to the DDR4 SDRAM de-
vices, which helps enable higher densities and increase signal integrity. The RCD also
provides a low-jitter, low-skew PLL that redistributes a differential clock pair to multiple
differential pairs of clock outputs.

Control Words

The RCD device(s) used on DDR4 RDIMMs, LRDIMMs, and NVDIMMs contain configu-
ration registers known as control words, which the host uses to configure the RCD
based on criteria determined by the module design. Control words can be set by the
host controller through either the DRAM address and control bus or the I

2

C bus inter-

face. The RCD I

2

C bus interface resides on the same I

2

C bus interface as the module

temperature sensor and EEPROM.

Parity Operations

The RCD includes a parity-checking function that can be enabled or disabled in control
word RC0E. The RCD receives a parity bit at the DPAR input from the memory control-
ler and compares it with the data received on the qualified command and address in-
puts; it indicates on its open-drain ALERT_n pin whether a parity error has occurred. If
parity checking is enabled, the RCD forwards commands to the SDRAM when no parity
error has occurred. If the parity error function is disabled, the RCD forwards sampled
commands to the SDRAM regardless of whether a parity error has occurred. Parity is al-
so checked during control word WRITE operations unless parity checking is disabled.

Rank Addressing

The chip select pins (CS_n) on Micron's modules are used to select a specific rank of
DRAM. The RDIMM is capable of selecting ranks in one of three different operating
modes, dependant on setting DA[1:0] bits in the DIMM configuration control word lo-
cated within the RCD. Direct DualCS mode is utilized for single- or dual-rank modules.
For quad-rank modules, either direct or encoded QuadCS mode is used.

16GB (x72, ECC, DR) 288-Pin DDR4 RDIMM

Registering Clock Driver Operation

CCMTD-1725822587-9899
asf18c2gx72pdz.pdf - Rev. H 7/19 EN

14

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