MCF5307AI90B Datasheet, PDF (238/484 Pages) Freescale Semiconductor, Inc – Integrated Microprocessor

Freescale Semiconductor, Inc.
Asynchronous Operation
11.3 Asynchronous Operation
The DRAM controller supports asynchronous DRAMs for cost-effective systems. Typical
access times for the DRAM controller interfacing to ADRAM are 4-3-3-3. The DRAM
controller supports the following four asynchronous modes:
• Non-page mode
• Burst page mode
• Continuous page mode
• Extended data-out mode
In asynchronous mode, RAS and CAS always transition at the falling clock edge. As
summarized previously, operation and timing of each ADRAM block is controlled by
separate registers, but refresh is the same for both. All ADRAM accesses should be
terminated by the DRAM controller. There is no priority encoding between memory
blocks, so programming blocks to overlap with other blocks or with other internal resources
causes undefined behavior.
11.3.1 DRAM Controller Signals in Asynchronous Mode
Table 11-2 summarizes DRAM signals used in asynchronous mode.
Table 11-2. SDRAM Signal Summary
Signal
RAS[1:0]
CAS[3:0]
DRAMW
Description
Row address strobes. Interface to RAS inputs on industry-standard ADRAMs. When SDRAMs are used,
these signals interface to the chip-select lines within an SDRAM’s memory block. Thus, there is one RAS
line for each of the two blocks.
Column address strobes. Interface to CAS inputs on industry-standard DRAMs. These provide CAS for
a given ADRAM block. When SDRAMs are used, CAS[3:0] control the byte enables (DQMx) for standard
SDRAMs. CAS[3:0] strobes data in least-to-most significant byte order (CAS0 is MSB).
DRAM read/write. Asserted when a DRAM write cycle is underway. Negated for read bus cycles.
11.3.2 Asynchronous Register Set
The following register configurations apply when DCR[SO] is 0, indicating the DRAM
controller is interfacing to asynchronous DRAMs.
11.3.2.1 DRAM Control Register (DCR) in Asynchronous Mode
The DCR provides programmable options for the refresh logic as well as the control bit to
determine if the module is operating with synchronous or asynchronous DRAMs. The DCR
is shown in Figure 11-2.
11-4
MCF5307 User’s Manual
For More Information On This Product,
Go to: www.freescale.com