Motorola MSC8101 ADS User's Guide Page 89

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Connecting the Bus to the SDRAM Memory Interface
Connecting External Memories and Memory-Mapped Devices 4-13
4.4.5 PowerPC 60x Bus Mode SDRAM Hardware Interconnection
In PowerPC Multi-Master Bus mode, there are separate address and data tenure phases in
which the address is not driven for the entire bus transaction, so internal address
multiplexing is not used. Therefore, external logic must latch the address and multiplex
the column and row addresses to the SDRAM at the appropriate time. The MSC8101
memory controller provides an Address Latch Enable (
ALE) and Select pin (SDAMUX) to
control these functions. Figure 4-10 shows the interconnection between the MSC8101
and the 32-bit Samsung K4S643232C using page-based interleaving and PowerPC
Multi-Master Bus mode.
The interface signals are essentially the same as for Single-Master MSC8101 Bus mode,
apart from the address portion. While separate latch and multiplexor devices could be
used, this example uses a 74LVT16260, which has an integrated latch and 24:12
multiplexor. As Figure 4-6, MSC8101 SDRAM Address Multiplexing, on page 4-9 shows,
addresses A[22–29] are used during column accesses and A[9–19] are used for row
accesses. As A9 is output on the
SDA10 pin, the connection to the multiplexor is A[10–19]
and A[22–29], respectively. The bank address lines are output on the
BNKSEL lines. The LE
pin latches the 1B and 2B inputs on the falling edge of the
ALE signal; the output of the
multiplexor is determined by the MSC8101
PSDAMUX pin.
Figure 4-10. MSC8101-To-SDRAM Interconnection in PowerPC 60x Multi-Master Bus
Mode
MSC8101
MSC8101 SDRAM
PSDDQM[0–3]
A[19–10]
D[0–31]
CS2
PSDRAS
PSDCAS
A10/AP
K4S643232C
SDRAM
DLLIN
CS
BNKSEL[2–1]
A[0–9]
PSDA10
CLKIN
A[29–22]
ALE
Multiplex
Latch
74LVT16260
PSDAMUX
SELLE1B
1B[1–10]
2B[1-8]
A[1–10]
LE2B
LEA1B
LEA2B
OE1B
OE2B
OEA
+3.3V
CLKOUT
RAS
CAS
WE
DQM[0–3]
BA[0–1]
D[0–31]
CLK
PSDWE
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