Motorola MPC8240, Руководство пользователя

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6-46 MPC8240 Integrated Processor User’s Manual
FPM or EDO DRAM Interface Operation
6.3 FPM or EDO DRAM Interface Operation
Figure 6-29 shows an internal block diagram of the FPM and EDO DRAM interface for the
MPC8240.
Figure 6-29. FPM or EDO DRAM Memory Interface Block Diagram
The MPC8240 supports a variety of DRAM configurations, through SIMM, DIMM, or
direct board attachment. Thirteen address pins provide for DRAM device densities of up to
64 Mbits. Eight row address strobe (RAS) signals support up to eight banks of memory.
Each bank can be 8 bytes wide; eight column address strobe (CAS) signals are used to
provide byte selection for writes. The banks can be built of DRAMs, SIMMs or DIMMs
that range from 4 to 128 Mbits as described in Table 6-17. The memory design must be
byte-selectable for writes using CAS. The MPC8240 allows up to 1 Gbyte of addressable
memory.
In addition to the CAS[0:7] signals, RAS[0:7] signals, and address signals SDMA[12:0]
and SDBA[1:0], there are 64 data signals MDH[0:31] and MDL[0:31], a write enable (WE)
signal, and one parity bit per byte-width of data PAR[0:7] for a total of 102 DRAM memory
signals. Figure 6-30 is an example of a two-bank 16-Mbyte DRAM system. Figure 6-31
shows an example DRAM organization.
DRAM
ECC
DRAM
Address
Address
(Processor or PCI)
DRAM Memory Control
Processor data to DRAM
Processor data from DRAM
DRAM write output enable
Central Control Unit
FPM or EDO DRAM Memory Interface
SDMA[12:0]
RAS[0:7]
CAS[0:7]
PAR[0:7]
DRAM Memory Array
Data
MDH[0:31]
MDL[0:31]
Control
MUX
Row
Col
Note: selectable
Flow Through Buffering
Error Checking
•64-bit ECC (No In-line ECC)
•Parity