PXR40RM Datasheet, PDF (347/1434 Pages) Freescale Semiconductor, Inc – PXR40 Microcontroller

Chapter 11
General-Purpose Static RAM (SRAM)
11.1 Introduction
The SRAM provides 256 KB of general-purpose static RAM (SRAM). The first 32 KB of SRAM is
powered by a separate power supply pin for standby operation. Figure 11-1 shows the internal SRAM
block diagram.
SRAM
32 KB
Standby SRAM
V_STBY
Figure 11-1. Internal SRAM Block Diagram
The SRAM controller has these features:
• Read/write accesses can map to SRAM from any master
• 32 KB with a separate power source for standby operation
• Byte, halfword, word, and doubleword addressable
• 8-bit ECC
11.2 SRAM Operating Modes
Table 11-1 lists and describes the SRAM operating modes.
Table 11-1. SRAM Operating Modes
Mode
Normal (functional)
Standby
Description
Allows reads and writes of SRAM.
Preserves the 32 KB of standby memory when the V_DD (1.5 V) power drops below the level of
V_STBY (0.8–1.2 V). Updates to standby SRAM are inhibited during system reset or during standby
mode.
11.3 External Signal Description
The external signal for SRAM is the V_STBY RAM power supply. If the standby feature of the SRAM is
not used, tie the V_STBY pin to V_SS.
Freescale Semiconductor
PXR40 Microcontroller Reference Manual, Rev. 1
11-1