SPMCK16Z4MPV20 datasheet(400/500 Pages) FREESCALE

400 / 500 page

M68HC16 Z SERIES

D-26

USER’S MANUAL

BOOT — Boot ROM Control

Reset state of BOOT is specified at mask time. This is a read-only bit.

0 = ROM responds to bootstrap word locations during reset vector fetch.

1 = ROM does not respond to bootstrap word locations during reset vector fetch.

Bootstrap operation is overridden if STOP = 1 at reset.

LOCK — Lock Registers

The reset state of LOCK is specified at mask time. If the reset state of the LOCK is

zero, it can be set once after reset to allow protection of the registers after initialization.

Once the LOCK bit is set, it cannot be cleared again until after a reset. LOCK protects

the ASPC and WAIT fields, as well as the ROMBAL and ROMBAH registers. ASPC,

ROMBAL and ROMBAH are also protected by the STOP bit.

0 = Write lock disabled. Protected registers and fields can be written.

1 = Write lock enabled. Protected registers and fields cannot be written.

EMUL — Emulation Mode Control

0 = Normal ROM operation

1 = Accesses to the ROM array are forced external, allowing memory selected by

the CSM pin to respond to the access.

Because the MC68HC16Z2 and the MC68HC16Z3 do not support ROM emulation

mode, this bit should never be set.

ASPC[1:0] — ROM Array Space

The ASPC field limits access to the SRAM array in microcontrollers that support sep-

arate user and supervisor operating modes. ASPC1 has no effect because the CPU16

operates in supervisor mode only. This bit may be read or written at any time. The

reset state of ASPC[1:0] is specified at mask time. Table D-22 shows ASPC[1:0] en-

coding.

WAIT[1:0] — Wait States Field

WAIT[1:0] specifies the number of wait states inserted by the MRM during ROM array

accesses. The reset state of WAIT[1:0] is user specified. The field can be written only

if LOCK = 0 and STOP = 1. Table D-23 shows the wait states field.

Table D-22 ROM Array Space Field

ASPC[1:0]

State Specified

Program and data accesses

Program access only

Table D-23 Wait States Field

WAIT[1:0]

Number of

Wait States

Clocks per Transfer

–1

Freescale Semiconductor, Inc.

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