![](http://datasheet.mmic.net.cn/290000/XPC801ZP25_datasheet_16187868/XPC801ZP25_290.png)
Memory Controller
MOTOROLA
MPC801 USER’S MANUAL
15-3
15
15.2 BASIC ARCHITECTURE
The memory controller consists of three machines:
General-purpose chip-select machine
User-programmable machine A
User-programmable machine B
Each bank can be assigned to any one of these machines via the MS bits in the base register
as illustrated in Figure 15-3. When an access to one of the memory banks is initiated, the
corresponding machine takes ownership of the external signals that control access until the
cycle terminates. The general-purpose chip-select machine provides a glueless interface to
EPROM, SRAM, Flash EPROM, and other peripherals. The general-purpose chip-selects
are available on the CS[0:7] signals. CS0 is also the global (boot) chip-select that is used to
access the boot EPROM. The chip-select allows 0 to 30 wait states.
Some features are common to all eight memory banks. The full 32-bit decode is available,
even if all 32 address bits are not visible outside the MPC801. Since there is only a 26-bit
address bus, the memory controller related to the external master address has a 32-bit
address whose six most-significant bit s are equal to 0. The memory controller only uses 17
most-significant bit addresses for address decoding. Each memory bank includes a variable
block size of 32K or 64K at a maximum of 256M. Parity can be generated and checked for
any memory bank and each memory bank can be selected for read-only or read/write
operation. For system protection purposes, accessing a memory bank can be restricted to
certain address type codes. For additional flexibility, address type comparison provides a
mask option.
The memory controller functionality allows the design of MPC801-based systems with little
or no glue logic required. In Figure 15-2, CS0
is used for the 32-bit DRAM as the RAS signal. The BS_A[0:3] signals are used as the CAS
signals on the DRAM.
is used as the 16-bit boot EPROM and CS1