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IDT DDR Controller
DDR Registers
79RC32438 User Reference Manual
7 - 8
November 4, 2002
Notes
AP
Description:
Auto Precharge Enable.
This field controls the value driven on Auto Precharge (shown as “AP”
in Tables 7.3 and 7.4) bit during DDR transactions. If auto precharge is enabled, the row being
accessed is precharged at the completion of a read or write transaction.
0 Auto precharge disabled (AP=0).
1 Auto precharge enabled (AP=1).
Initial Value:
0x1
(this field is not modified due to a warm reset)
Read Value:
Previous value written
Write Effect:
Modify value
RCD
Description:
Active to Read or Write Delay.
This field specifies the minimum number of DDR clock cycles
between the issuing of a DDR ACTIVE command and a READ or WRITE command.
0 1 clock cycle
1 2 clock cycles
2 3 clock cycles
3 4 clock cycles
Initial Value:
0x2
(this field is not modified due to a warm reset)
Read Value:
Previous value written
Write Effect:
Modify value
CL
Description:
CAS Latency.
This field contains the CAS latency value in DDR clock cycles.
0 2 clock cycles
1 2.5 clock cycles
2 3 clock cycles
3 4 clock cycles
Initial Value:
0x2
(this field is not modified due to a warm reset)
Read Value:
Previous value written
Write Effect:
Modify value
DBM
Description:
Data Bus Multiplexing.
When this bit is set, data bus multiplexing is enabled. For more informa-
tion, refer to the DDR Data Bus Multiplexing section in this chapter.
Initial Value:
0x0
(this field is not modified due to a warm reset)
Read Value:
Previous value written
Write Effect:
Modify value
SDS
Description:
Single Data Strobe.
The DDR controller normally operates with a DDR data strobe per byte lane
(i.e., DDRDQS[1:0] in 16-bit data bus width mode and DDRDQS[3:0] in 32-bit data bus width
mode). Some DDR devices have a single data byte strobe for ALL byte lanes. When this bit is
set, DDRDQS[0] is used for all byte lanes.
Initial Value:
0x0
(this field is not modified due to a warm reset)
Read Value:
Previous value written
Write Effect:
Modify value