SPMCK16Z4MPV20 datasheet(179/500 Pages) FREESCALE

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M68HC16 Z SERIES

STANDBY RAM MODULE

USER’S MANUAL

6-1

SECTION 6

STANDBY RAM MODULE

The standby RAM (SRAM) module consists of a fixed-location control register block

and an array of fast (two clock) static RAM that may be mapped to a user specified

location in the system memory map. Array size depends on the M68HC16, M68CK16,

and M68CM16 Z-series version. Refer to Table 6-1 for appropriate SRAM array size.

The SRAM is especially useful for system stacks and variable storage.

The SRAM can be mapped to any address that is a multiple of the array size so long

as SRAM boundaries do not overlap the module control registers (overlap makes the

registers inaccessible). Data can be read/written in bytes, words or long words. SRAM

is powered by VDD in normal operation. During power-down, SRAM contents can be

maintained by power from the VSTBY input. Power switching between sources is auto-

matic.

6.1 SRAM Register Block

There are four SRAM control registers: the RAM module configuration register (RAM-

MCR), the RAM test register (RAMTST), and the RAM array base address registers

(RAMBAH/RAMBAL).

The module mapping bit (MM) in the SIM configuration register (SIMCR) defines the

most significant bit (ADDR23) of the IMB address for each M68HC16, M68CK16, and

M68CM16 Z-series module. Because ADDR[23:20] are driven to the same value as

ADDR19, MM must be set to one. If MM is cleared, IMB modules are inaccessible. For

more information about how the state of MM affects the system, refer to 5.2.1 Module

Mapping.

The SRAM control register consists of eight bytes, but not all locations are implement-

ed. Unimplemented register addresses are read as zeros, and writes have no effect.

Refer to D.3 Standby RAM Module for the register block address map and register

bit/field definitions.

Table 6-1 SRAM Configuration

Z-Series Device

Array Size

MC68HC16Z1

MC68CK16Z1

MC68CM16Z1

MC68HC16Z4

MC68CK16Z4

1 Kbyte

MC68HC16Z2

2 Kbytes

MC68HC16Z3

4 Kbytes

Freescale Semiconductor, Inc.

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