mc68hc916y3 Freescale Semiconductor, Inc, mc68hc916y3 Datasheet - Page 189

• Manufacturer Part Number: mc68hc916y3
• Description: Mc68hc16y3 16 Bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

7.1 MRM Register Block
7.2 MRM Array Address Mapping
MC68HC16Y3/916Y3
USER’S MANUAL
The masked ROM module (MRM) is used only in the MC68HC16Y3. It consists of two
fixed-location control register blocks and a 64-Kbyte and a 32-Kbyte array, for a total
of 96 K-bytes of mask-programmed read-only memory that can be mapped to any 96-
Kbyte boundary in the system memory map. The MRM can be programmed to insert
wait states to accommodate migration from slow external development memory. Ac-
cess time depends upon the number of wait states specified, but can be as fast as two
clock cycles. The MRM can be used for program accesses only, or for program and
data accesses. Data can be read in bytes, words or long words. The MRM can be con-
figured to support system bootstrap during reset.
There are three MRM control registers: the masked ROM module configuration regis-
ter (MRMCR), and the ROM array base address registers (ROMBAH and ROMBAL).
In addition, the MRM register block contains signature registers (SIGHI and SIGLO),
and ROM bootstrap words (ROMBS[0:3]).
The module mapping bit (MM) in the SCIMCR defines the most significant bit
(ADDR23) of the IMB address for each MC68HC16R1/916R1 module. Because the
CPU16 drives only ADDR[19:0] and ADDR[23:20] follow the logic state of ADDR19,
MM must equal one. 5.2.1 Module Mapping contains information about how the state
of MM affects the system.
Both MRM control register blocks consist of 32 bytes, but not all locations are imple-
mented. Unimplemented register addresses are read as zeros, and writes have no ef-
fect. Refer to D.4 Masked ROM Module for register block address map and register
bit/field definitions.
Base address registers ROMBAH and ROMBAL are used to specify the ROM array
base address in the memory map. Although the base address contained in ROMBAH
and ROMBAL is mask-programmed, these registers can be written after reset to
change the default array address if the base address lock bit (LOCK in MRMCR) is not
masked to a value of one.
The MRM array can be mapped to any 96-Kbyte boundary in the memory map, but
must not overlap other module control registers (overlap makes the registers inacces-
sible). If the array overlaps the MRM register block, addresses in the block are access-
ed instead of the corresponding 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.
SECTION 7MASKED ROM MODULE
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MASKED ROM MODULE
MOTOROLA
7-1