Zynq-7000 AP SoC and 7 Series FPGAs MIS v4.1
140
UG586 November 30, 2016
Chapter 1:
DDR3 and DDR2 SDRAM Memory Interface Solution
Command Path
A command requested by the calibration logic or Memory Controller is sent out as a PHY
control word to the PHY control block and a simultaneous input to the
address/control/command OUT_FIFOs. Each of the address/control/command signals must
have values for four memory clock cycles because each PHY_Clk cycle entails four memory
clock cycles.
There are three types of commands:
• Write commands including write and write with auto precharge. The PHY command
values in the PHY control word for both these write commands are the same (
0x01
).
The difference is the address value input to the OUT_FIFO. Address bit A10 is 1 for
writes with auto precharge in the address OUT_FIFOs.
• Read commands including read and read with auto precharge. The PHY command
values in the PHY control word for both these read commands are the same (
0x11
). The
difference is the address value input to the OUT_FIFO. Address bit A10 is 1 for reads
with auto precharge in the address OUT_FIFOs.
• Non-Data commands including Mode Register Set, Refresh, Precharge, Precharge All
Banks, Activate, No Operation, Deselect, ZQ Calibration Long, and ZQ Calibration Short.
The PHY command values in the PHY control word for all these commands are the same
(
0x100
). The
RAS_N
,
CAS_N
,
WE_N
, bank address, and address values input to the
OUT_FIFOs associated with these commands differ.
shows the block diagram of the address/control/command path. The OSERDES
is used in single data rate (SDR) mode because address/control/commands are
SDR
signals.
A PHY control word is qualified with the
PHY_Ctl_Wr_N
signal and an entry to the
OUT_FIFOs is qualified with the
PHY_Cmd_WrEn
signal. The FPGA logic need not issue NOP
commands during long wait times between valid commands to the PHY control block
because the default in the dedicated PHY for address/commands can be set to
0
or
1
as
needed.