MC68HC16Z1CAG16 Datasheet, PDF (184/500 Pages) Freescale Semiconductor, Inc – M68HC16Z Series users manual

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The MRM array can be mapped to any 8-Kbyte boundary in the memory map, but must
not overlap other module control registers (overlap makes the registers inaccessible).
If the array overlaps the MRM register block, addresses in the register block are ac-
cessed instead of the corresponding ROM array addresses.
ROMBAH and ROMBAL can only be written while the ROM is in low-power stop mode
(MRMCR STOP = 1) and the base address lock (MRMCR LOCK = 0) is disabled.
LOCK can be written once only to a value of one; subsequent writes are ignored. This
prevents accidental remapping of the array.
7.3 MRM Array Address Space Type
ASPC[1:0] in MRMCR determines ROM array address space type. The module can
respond to both program and data space accesses or to program space accesses
only. The default value of ASPC[1:0] is established during mask programming, but the
value can be changed after reset if the LOCK bit in the MRMCR has not been masked
to a value of one. Because the CPU16 operates in supervisor mode only, ASPC1 has
no effect.
Table 7-1 shows ASPC[1:0] field encodings.
Table 7-1 ROM Array Space Field
ASPC[1:0]
X0
X1
State Specified
Program and data accesses
Program access only
Refer to 5.5.1.7 Function Codes for more information concerning address space
types and program/data space access. Refer to 4.6 Addressing Modes for more in-
formation on addressing modes.
7.4 Normal Access
The array can be accessed by byte, word, or long word. A byte or aligned word access
takes a minimum of one bus cycle (two system clocks). A long word or misaligned
word access requires a minimum of two bus cycles.
Access time can be optimized for a particular application by inserting wait states into
each access. The number of wait states inserted is determined by the value of
WAIT[1:0] in the MRMCR. Two, three, four, or five clock accesses can be specified.
The default value WAIT[1:0] is established during mask programming, but field value
can be changed after reset if the LOCK bit in the MRMCR has not been masked to a
value of one.
Table 7-2 shows WAIT[1:0] field encodings.
MASKED ROM MODULE
M68HC16 Z SERIES
7-2
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