7-2
MCF5249UM
MOTOROLA
DRAM Controller Operation
Figure 7-1 Synchronous DRAM Controller Block Diagram
The DRAM controller’s major components, shown in
Figure 7-1, are described as follows:
DRAM address and control registers (DACR0 and DACR1)—The DRAM controller consists of two
configuration register units, one for each supported memory block. DACR0 is accessed at MBAR +
0x0108; DACR1 is accessed at 0x0110. The register information is passed on to the hit logic.
Control logic and state machine—Generates all DRAM signals, taking bus cycle characteristic data
from the block logic, along with hit information to generate DRAM accesses. Handles refresh
requests from the refresh counter.
—
DRAM control register (DCR)—Contains data to control refresh operation of the DRAM
controller. Both memory blocks are refreshed concurrently as controlled by DCR[RC].
—
Refresh counter—Determines when refresh should occur, determined by the value of
DCR[RC]. It generates a refresh request to the control block.
Hit logic—Compares address and attribute signals of a current DRAM bus cycle to both DACRs to
determine if a DRAM block is being accessed. Hits are passed to the control logic along with
characteristics of the bus cycle to be generated.
Page hit logic—Determines if the next DRAM access is in the same DRAM page as the previous one.
This information is passed on to the control logic.
Address multiplexing—Multiplexes addresses to allow column and row addresses to share pins. This
allows glueless interface to DRAMs.
7.2
DRAM CONTROLLER OPERATION
7.2.1
DRAM CONTROLLER REGISTERS
The DRAM controller registers memory map is shown in
Table 7-1Memory Block 0 Hit Logic
DRAM Address/Control Register 0
(DACR0)
A25, A[23:1]
Internal
Address
Control Logic
and
DRAM Controller Module
Refresh Counter
State Machine
Multiplexing
Page Hit
Logic
DRAM Control
Register (DCR)
Bus
Memory Block 1 Hit Logic
DRAM Address/Control Register 1
(DACR1)
A[31:0]
SDRAM_CS1
SDRAM_CS2
SDRAS
SDCAS
SDWE
SDUDQM
SDLDQM
BCLKE
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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