This 25-bit 1:1 or 14-bit 1:2 configurable registered buffer is designed for 1.7-V to 1.9-V V_CC operation. In the 1:1 pinout configuration, only 1 device per DIMM is required to drive 9 SDRAM loads. In the 1:2 pinout configuration, 2 devices per DIMM are required to drive 18 SDRAM loads.

All inputs are SSTL_18, except the reset (RESET) and control (Cn) inputs which are LVCMOS. All outputs are edge-controlled circuits optimized for unterminated DIMM loads and meet SSTL_18 specifications, except the open-drain error (QERR) output.

The SN74SSTU32866A buffer operates from a differential clock (CLK and CLK). Data are registered at the crossing of CLK going high and CLK\ going low.

The SN74SSTU32866A buffer accepts a parity bit from the memory controller on the parity bit (PAR_IN) input, compares it with the data received on the DIMM-independent D-inputs (D2-D3, D5-D6, D8-D25 when C0 = 0 and C1 = 0; D2-D3, D5-D6, D8-D14 when C0 = 0 and C1=1; or D1-D6, D8-D13 when C0 = 1 and C1 = 1) and indicates whether a parity error has occurred on the open-drain QERR pin (active low). The convention is even parity; i.e., valid parity is defined as an even number of ones across the DIMM-independent data inputs, combined with the parity input bit. To calculate parity, all DIMM-independent data inputs must be tied to a known logic state.

When used as a single device, the C0 and C1 inputs are tied low. In this configuration, parity is checked on the PAR_IN input signal, which arrives one cycle after the input data to which it applies. Two clock cycles after the data are registered, the corresponding partial-parity-out (PPO) and QERR signals are generated.