MPC755 datasheet(17/56 Pages) NXP

17 / 56 page

MPC755 RISC Microprocessor Hardware Specifications, Rev. 8

Freescale Semiconductor

Electrical and Thermal Characteristics

SRAM. Note that revisions of the MPC755 prior to Rev. 2.8 (Rev. E) were limited in performance, and

were typically limited to 175 MHz with similarly-rated SRAM. For more information, see Section 10.2,

“Part Numbers Not Fully Addressed by This Document.”

Freescale is similarly limited by system constraints and cannot perform tests of the L2 interface on a

socketed part on a functional tester at the maximum frequencies of Table 11. Therefore, functional

operation and AC timing information are tested at core-to-L2 divisors of 2 or greater. Functionality of

core-to-L2 divisors of 1 or 1.5 is verified at less than maximum rated frequencies.

L2 input and output signals are latched or enabled, respectively, by the internal L2CLK (which is SYSCLK

multiplied up to the core frequency and divided down to the L2CLK frequency). In other words, the AC

timings of Table 12 and Table 13 are entirely independent of L2SYNC_IN. In a closed loop system, where

L2SYNC_IN is driven through the board trace by L2SYNC_OUT, L2SYNC_IN only controls the output

phase of L2CLK_OUTA and L2CLK_OUTB which are used to latch or enable data at the SRAMs.

However, since in a closed loop system L2SYNC_IN is held in phase alignment with the internal L2CLK,

the signals of Table 12 and Table 13 are referenced to this signal rather than the not-externally-visible

internal L2CLK. During manufacturing test, these times are actually measured relative to SYSCLK.

The L2SYNC_OUT signal is intended to be routed halfway out to the SRAMs and then returned to the

L2SYNC_IN input of the MPC755 to synchronize L2CLK_OUT at the SRAM with the processor’s

internal clock. L2CLK_OUT at the SRAM can be offset forward or backward in time by shortening or

lengthening the routing of L2SYNC_OUT to L2SYNC_IN. See Freescale Application Note AN1794/D,

Backside L2 Timing Analysis for PCB Design Engineers.

The L2CLK_OUTA and L2CLK_OUTB signals should not have more than two loads.

MPC755 Datasheet(PDF) 17 Page - NXP Semiconductors