Memory Controller
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
15-7
15.3.1
Address Space Programming
Each bank has an option register (ORx) and a base register (BRx), which contains a V bit that indicates
that the information for the chip-select is valid.
Each base register defines the starting address of its memory bank and each option register defines the
attributes for its memory bank. Option registers also define the initial address multiplexing for a memory
cycle controlled by a UPM. Each time an internal or external bus cycle access is requested, the address and
its corresponding address type are compared to each bank. If one bank matches, its attributes defined in
BRx and ORx control the memory access. If multiple matches occur, the lowest numbered matched bank
handles the access.
15.3.2
Register Programming Order
For UPM-controlled chip selects, UPM registers should be programmed before ORx and BRx. For all chip
selects, ORx should be programmed before BRx except when programming the boot chip select (CS0)
after hardware reset, in which case, BR0 should be programmed before OR0.
15.3.3
Memory Bank Write Protection
Attempting to write to an address range marked restricted in BRx[WP] causes a write-protect violation for
which MSTAT[WPER] is set.
15.3.4
Address Type Protection
BRx[AT] and ORx[ATM] can be used to implement address-type protection in a manner similar to the
address space programming. Note that when external masters access memory controller-managed slaves
on the bus, the internal AT[0:2] signals to the memory controller are forced to 0b100.
15.3.5
8-, 16-, and 32-Bit Port Size Configuration
The port size is specified by BRx[PS]. Eight-bit ports must be connected to D[0:7], 16-bit ports must be
connected to D[0:15]. For ports smaller than 32-bits, dynamic bus sizing is performed for all internal
masters, such that only external bus accesses result, such as those defined in
Table 15-2
.
Table 15-2. Access Granularities for Predefined Port Sizes
Predefined
Port Size
Bytes
Half Words
Words (on Word
Boundaries)
Odd
Even
Odd
Even
8-bit
√
√
—
—
—
16-bit
√
√
—
√
(on D[0:15])
—
32-bit
√
√
√
√
√
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