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2.3
Signal Descriptions
DDR_D[31:0]
DDR2
memory
controller
DDR_CLK
DDR_CLK
DDR_CS
DDR_CKE
DDR_RAS
DDR_WE
DDR_DQM[3:0]
DDR_CAS
DDR_BA[2:0]
DDR_DQS[3:0]
DDR_A[12:0]
DDR_ZN
DDR_ZP
200
Ω
200
Ω
Peripheral Architecture
The DDR2 memory controller signals are shown in
Figure 3
and described in
Table 2
. The following
features are included:
•
The maximum data bus is 32-bits wide.
•
The address bus is 13-bits wide with an additional 3 bank address pins.
•
Two differential output clocks driven by internal clock sources.
•
Command signals: Row and column address strobe, write enable strobe, data strobe, and data mask.
•
One chip select signal and one clock enable signal.
Figure 3. DDR2 Memory Controller Signals
Table 2. DDR2 Memory Controller Signal Descriptions
Pin
Type
Description
DDR_CLK,
O/Z
Clock:
Differential clock outputs.
DDR_CLK
DDR_CKE
O/Z
Clock enable:
Active high.
DDR_CS
O/Z
Chip select:
Active low.
DDR_WE
O/Z
Write enable strobe:
Active low, command output.
DDR_RAS
O/Z
Row address strobe:
Active low, command output.
DDR_CAS
O/Z
Column address strobe:
Active low, command output.
DDR_DQM[3:0]
O/Z
Data mask
: Output mask signal for write data.
DDR_DQS[3:0]
I/O/Z
Data strobe:
Active high, bi-directional signals. Output with write data, input with read data.
DDR_BA[2:0]
O/Z
Bank address:
Output, defining which bank a given command is applied.
DDR_A[12:0]
O/Z
Address:
Address bus.
DDR_D[31:0]
I/O/Z
Data:
Bi-directional data bus. Input for read data, output for write data.
DDR_ZN,
O
Output impedance control:
Required to set the DDR2 output impedance. Connected by way of
DDR_ZP
a 200-ohm resistor to power and ground (see
Figure 3
). The resistor should be chosen to be
4 times the desired impedance of the output buffer. By changing the size of the resistor, the
DDR2 outputs can be tuned to match the board load, if necessary.
SPRU986B – November 2007
DDR2 Memory Controller
11
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