SDRAM Controller (SDRAMC)
MCF52277 Reference Manual, Rev. 1
Freescale Semiconductor
19-5
19.3
Interface Recommendations
19.3.1
Supported Memory Configurations
The SDRAM controller supports up to 14 row addresses and up to (13 in 16-bit bus mode) column
addresses. However, the maximum row and column addresses are not simultaneously supported. The
number of row and column addresses must be less than or equal to 24 (25 in 16-bit bus mode). In addition
to row/column address lines, there are always two row bank address bits. Therefore, the greatest possible
address space accessed using a single chip select is 2
26
x 32 bit (2
27
x 16 bit) or 256 MBytes.
show the address multiplexing used by the memory controller for different
configurations. When the SDRAM controller receives the internal module enable, it latches the internal
bus address lines IA[27:0] (IA equals internal address) and multiplexes them into row, column, and bank
addresses (RA, CA, and BA respectfully). In 32-bit bus mode, IA[9:2] are used for CA[7:0]. In 16-bit
mode, IA[9:1] are used for CA[8:0]. IA[11:10] are always used for BA[1:0], and IA[23:12] are always
used for RA[11:0]. IA[27:24] can be used for additional row or column address bits, as needed. The
additional row- or column-address bits are programmed via the SDCR[ADDR_MUX] bits.
NOTE
When the SDRAMC is configured to support an external 32-bit data bus. It
is not possible to connect a smaller device(s) to only part of the SDRAM’s
data bus. For example, if 16-bit wide devices are used, then user must use
two 16-bit devices connected as a 32-bit port.
SD_DQS[3:2]
I/O Edge-aligned with read data, centered in write data, captures data. The address correspondence:
SD_DQS3 - SD_D[31:24]
SD_DQS2 - SD_D[23:16]
Note:
If a read is attempted from a DDR SDRAM chip select when there is no memory to respond with the
appropriate SD_DQS pulses, the bus cycle hangs. Because there is no high level bus monitor on the
device, a reset is the only way to exit this error condition.
State
Meaning
Asserted — Similar to a clock signal, the edges are more important than being asserted or
negated.
High impedance — Depending on the SDCFG1[OE_RULE] bit, the SD_DQS can be in high
impedance until a write is occurring or only when a read is occurring.
Timing
Assertion/Negation — Occurs on crossing of SD_CLK and SD_CLK.
SD_WE
O
Command input. Along with SD_CS, SD_CAS, and SD_RAS defines the current command.
State
Meaning
Please see
for SDRAM commands.
Timing
Assertion/Negation— Occurs synchronously with SD_CLK.
Table 19-1. SDRAM Interface—Detailed Signal Descriptions (continued)
Signal
I/O
Description
Содержание MCF52277
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