MPC555
/
MPC556
MEMORY CONTROLLER
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
10-3
From zero to 30 wait states can be programmed with TA generation. Four byte-write
and read-enable signals (WE/BE[0:3]) are available for each byte that is written to
memory. An output enable (OE) signal is provided to eliminate external glue logic. A
memory transfer start (MTS) strobe permits one master on a bus to access external
memory through the chip selects on another.
The memory controller functionality allows MPC555 / MPC556-based systems to be
built with little or no glue logic. A minimal system using no glue logic is shown in
. In this example CS[0]
is used for the 16-bit boot EPROM and CS[1]
is used for
the 32-bit SRAM. The WE/BE[0:3] signals are used both to program the EPROM and
to enable write access to various bytes in the RAM.
Figure 10-3 MPC555
/
MPC556 Simple System Configuration
10.2 Memory Controller Architecture
The memory controller consists of a basic machine that handles the memory access
cycle: the general-purpose chip-select machine (GPCM).
When a new access to external memory is requested by any of the internal masters,
the address of the transfer (with 17 bits having mask) and the address type (with 3 bits
having mask) are compared to each one of the valid banks defined in the memory con-
troller. Refer to
CE
OE
W
EPROM
Address
DATA[0:15]
SRAM
Address
CE
WE/BE[0:3]
Data
CS[1]
OE
Address
Data
CS[0]
WE/BE[0:3]
CE
OE
OE
[0:15]
[0:31]
WE/BE[0:1]
MPC555 / MPC556
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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