
MOTOROLA
5-48
SYSTEM INTERFACE UNIT
Rev. 15 June 98
MPC509
USER’S MANUAL
instructions to reconfigure the chip-select registers to provide multi-level protection
shortly after power-on.
5.5.7 Access Protection
The SUPV, DSP, and WP bits in the option registers for CSBOOT, the CSBOOT sub-
block, and CS[1:5] control access to the address block assigned to the chip select.
These bits are present in the option registers for chip selects with address decoding
logic only; they are not present in the option registers for CS0 or CS[6:11]. In addition,
the bits take effect only if the chip select is programmed either as a CE or as a sub-
block.
If the chip-select unit detects a protection violation, it asserts the internal TEA signal
and does not assert the external chip enable signal. Assertion of TEA causes the pro-
cessor to enter the checkstop state, enter debug mode, or process a machine check
exception. Refer to the RCPU Reference Manual (RCPURM/AD) for details.
5.5.7.1 Supervisor Space Protection
The SUPV bit in the option registers for CSBOOT, the CSBOOT sub-block, and
CS[1:5] controls user-level access to the associated region. If the bit is set, access is
permitted at the supervisor privilege level only. If the bit is cleared, both supervisor-
and user-level accesses are permitted.
When an access is made to the region assigned to the chip select, the chip-select logic
compares the SUPV bit with the internal AT0 signal, which indicates whether the
access is at the user (AT0 = 0) or supervisor (AT0 = 1) privilege level. If the chip-select
logic detects a protection violation (SUPV = 1 and AT0 = 0), it asserts the internal TEA
signal and does not assert the external chip enable signal.
This protection applies to data address space only. The chip-select logic does not
check for supervisor access protection on instruction accesses.
5.5.7.2 Data Space Protection
The DSP bit in the option registers for CSBOOT, the CSBOOT sub-block, and CS[1:5]
controls whether instruction access is allowed to the address block associated with the
chip select. If DSP is set, the address block is designated as data space; no instruction
access is allowed. This feature can be used to prevent the system from inadvertently
executing instructions out of data space.
When an access is made to the region controlled by the chip select, the chip-select
logic compares the DSP bit with the internal AT1 signal, which indicates whether the
access is to instruction or data space. If the chip-select logic detects a protection vio-
lation (DSP = 1 and AT1 = 1), it asserts the internal TEA signal and does not assert
the external chip enable signal.
5.5.7.3 Write Protection
The WP bit in the option registers for CSBOOT, the CSBOOT sub-block, and CS[1:5]
controls whether the address block is write-protected. If WP is set, read accesses only