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Memory Controller
15-8
MPC801 USER’S MANUAL
MOTOROLA
15
Anywhere from 0 to 30 wait states can be programmed for TA generation. The WE signals
are available for each byte that is written to memory. An OE signal is provided to eliminate
external glue logic. The memory banks selected to operate with the general-purpose
chip-select machine have features unique to that machine. On system reset, a global (boot)
chip-select is available to provide a boot ROM chip-select before the system is fully
configured. Next, the banks selected to operate with the general-purpose chip-select
machine support an option to output the CS signal at different timings with respect to the
external address bus. CS can be output in one of the following configurations:
Simultaneous with an external address
One quarter of a clock later
One half of a clock later
This depends on the value of the ACS field, plus an additional cycle if the TRLX bit is set.
The general-purpose chip-select machine allows you to connect to devices that have long
disconnect times on data by delaying new bus transactions addressing other memory banks
for additional clock cycles. Finally, the banks selected to operate with the general-purpose
chip-select machine support external cycle termination by sensing the TA signal that is
asserted by the addressed external slave.
Figure 15-5. MPC801 GPCM–Memory Devices Interface
Figure 15-5 describes the basic connection between the MPC801 and a “static” memory
device. In this case, CS
x
is connected directly to the CE signal of the memory device. The
WE signals are connected to the respective W pin in the memory device where each WE
signal corresponds to a different data byte. As illustrated in Figure 15-6, the CS
the same as the address lines output. The strobes for the transaction are supplied by the
OE or WE signals, depending on the transaction direction (read or write). This CS timing is
generated when the ACS bits in the corresponding OR
x
timing is
x
are set to ‘00’.
MEMORY
MPC801
ADDRESS
CE
OE
W
DATA
ADDRESS
CSx
OE
WE
DATA