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
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 V
DD
in normal operation. During power-down, SRAM contents can be
maintained by power from the V
STBY
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
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
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
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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