Altera External Memory PHY Interface - Manual (Page 66)

3–50 Chapter 3: Functional Description—ALTMEMPHY (nonAFI)
Design Considerations
External Memory PHY Interface (ALTMEMPHY) (nonAFI) Megafunction User Guide © January 2010 Altera Corporation
For DDR SDRAM, the write latency is fixed at one memory clock cycle, but for DDR2
SDRAM, this value changes with the read CAS latency. As the controller is running at
half the rate of the memory clock, a latency change of one controller clock cycle is
actually two memory clock cycles. The ALTMEMPHY megafunction allows you to
dynamically insert an extra memory clock of delay in the address and command path
to compensate for this. The insertion of delay is controlled by the ADDR_CMD_ADD_1T
parameter and the ctl_add_1t_ac_lat signal. If ADDR_CMD_ADD_1T is set to the
Figure 3–15. Write Commands and Write Data (Full-Rate Controller)
Notes to Figure 3–15 :
(1) The DDR command shows the command comprised of the command signals (ctl_mem_ras_n_h, ctl_mem_cas_n_h, and
ctl_mem_we_n_h) seen at the ALTMEMPHY input. There can be more than one clock cycle of NOP between ACT to RD depending on the value
of t
RCD
parameter of your memory device.
(2) The DDR command shows the command comprised of the command signals (mem_ras_n_h, mem_cas_n_h, and mem_we_n_h) seen at
the memory interface.
phy_clk
ctl_mem_cs_n_h
ctl_mem_addr_h
ctl_mem_odt_h
DDR Command (1)
mem_clk
mem_addr
mem_odt
mem_dqs
mem_dq
ctl_mem_wdata_valid
DDR Command (2)
mem_cs_n
PHY Command Input
PHY Write Data Input
PHY Command Output
NOP WR NOP
local_write_req
ctl_mem_dqs_burst
WR NOP WR NOP WR NOP
0000 0008 0000 000c 0000 0010 0000
NOP WR NOP WR NOP WR NOP WR NOP
0004 0000 0000 0008 0000 000c 0000
NOP WR
0010 0000
000000 1... 4... 3... 7... 0... f... 0... 0... c... 0... 1... 3... 2... 7... e... 8... 000000
0000 0... 0... 1... 0... 1... 1... 0... 1... 1... 0... 1... 0... 0... 1... 0000
PHY Write Data Output
mem_dqs
ctl_mem_wdata
WR NOP
0004 0000
0000 0... 0... 0... 1... 1... 1... 0... 1... 0... 1... 0... 0... 000000
808bdae4ec55833a 8e7a
1... 0... 0...
473d 02f5 01f4 08f3 04f7 20eb 10fb 8e7a 40cb 808bdae4ec55833a
0... 0...