SDRAM Controller (SDRAMC)
MCF52277 Reference Manual, Rev. 1
19-4
Freescale Semiconductor
SD_CAS
O
Column address strobe/command input. Along with SD_CS, SD_RAS, and SD_WE, defines the current
command.
State
Meaning
for the SDRAM commands.
Timing
Assertion/Negation — Occurs synchronously with SD_CLK
SD_RAS
O
Row address strobe/command input. Along with SD_CS, SD_CAS, and SD_WE, defines the current
command.
State
Meaning
for SDRAM commands.
Timing
Assertion/Negation — Occurs synchronously with SD_CLK.
SD_CKE
O
Clock enable. SD_CKE must be maintained high throughout
READ
and
WRITE
accesses. SD_CKE negates
to put the SDRAM into low-power, self-refresh mode. Input buffers, excluding SD_CLK, SD_CLK, and
SD_CKE, are disabled during self-refresh.
State
Meaning
Asserted — Activates internal clock signals and device input buffers and output drivers.
Negated —Deactivates internal clock signals and device input buffers and output drivers.
Timing
Assertion — Asynchronous for self-refresh exit and for output disable
Negation — Occurs synchronously with SD_CLK
SD_CLK
SD_CLK
O
SD_CLK and SD_CLK are differential clock outputs. All address and control output signals are sent on the
crossing of the positive edge of SD_CLK and the negative edge of SD_CLK. Output data is referenced to
the crossing of SD_CLK and SD_CLK (both directions of crossing).
Timing
Command signals occur synchronously with the rising edge of this clock. Data signals can
change on the rising and falling edge of the clock.
SD_CS[1:0]
O
SD_CS provides external bank selection on systems with multiple banks. SD_CS is considered part of the
command code.
State
Meaning
Asserted — Commands for the selected chip occur
Negated — All commands are masked.
Timing
Assertion/Negation — Occurs synchronously with SD_CLK
SD_DATA[31:0]
I/O Data bus. In 16-bit DDR configuration, the memory device data bus is connected to SD_D[31:16] bits.
Timing
Assertion/Negation — Occurs on crossing of SD_CLK and SD_CLK.
High Impedance - Depending on the OE_RULE bit in SDCFG1, the SD_DATA bus can be in
high impedance until a write occurs or only when a read occurs.
SD_DQM[3:0]
O
Output mask signal for write data. During reads, SD_DQM may be driven high, low, or floating. The address
correspondence:
SD_DM3 - SD_D[31:24]
SD_DM2 - SD_D[23:16]
SD_DM1 - SD_D[15:8]
SD_DM0 - SD_D[7:0]
State
Meaning
Asserted — Data is written to SDRAM
Negation — Data is masked
Timing
Assertion/Negation — Occurs on crossing of SD_CLK and SD_CLK.
Table 19-1. SDRAM Interface—Detailed Signal Descriptions (continued)
Signal
I/O
Description
Содержание MCF52277
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