Zynq-7000 AP SoC and 7 Series FPGAs MIS v4.1
139
UG586 November 30, 2016
Chapter 1:
DDR3 and DDR2 SDRAM Memory Interface Solution
The PHY control block has several counters that are not enabled because the synchronous
mode is used where PHY_Clk is either 1/4 or 1/2 the frequency of the DDR2 or DDR3 SDRAM
clock frequency.
At every rising edge of PHY_Clk, a PHY control word is sent to the PHY control block with
information for four memory clock cycles worth of commands and a 2-bit Seq count value.
The write enable to the control FIFO is always asserted and no operation (NOP) commands
are issued between valid commands in the synchronous mode of operation. The Seq count
must be increased with every command sequence of four. The Seq field is used to
synchronize PHY control blocks across multiple I/O banks.
The DDR3 SDRAM
RESET_N
signal is directly controlled by the FPGA logic, not the PHY
control word. The DDR2 SDRAM
RESET_N
signal for RDIMM interfaces is directly controlled
by the FPGA logic, not the PHY control word. The PHY control block, in conjunction with the
PHASER_OUT, generates the write DQS and the DQ/DQS 3-state control signals during read
and write commands.
The PHY cmd field is set based on whether the sequence of four commands has either a
write, a read, or neither. The PHY cmd field is set to write if there is a write request in the
command sequence. It is set to read if there is a read request in the command sequence,
and it is set to non-data if there is neither a write nor a read request in the command
sequence. A write and a read request cannot be issued within a sequence of four
commands. The control offset field in the PHY control word defines when the command
OUT_FIFOs is read out and transferred to the IOLOGIC. The data offset defines when the
data OUT_FIFOs are read out with respect to the command OUT_FIFOs being read. For read
commands, the data offset is determined during calibration. The PHY control block assumes
that valid data associated with a write command is already available in the DQ OUT_FIFO
when it is required to be read out.
RD_CMD_OFFSET_3
Vector[5:0]
This attribute specifies how long in DDR2 or DDR3 SDRAM clock cycles
after the associated read command is executed that the auxiliary output
becomes active.
RD_DURATION_3
Vector[5:0]
This attribute specifies how long in DDR2 or DDR3 SDRAM clock cycles
the auxiliary output remains active for a read command.
CMD_OFFSET
Vector[5:0]
This attribute specifies how long in DDR2 or DDR3 SDRAM clock cycles
after the associated command is executed that the auxiliary output
defined by AO_TOGGLE toggles.
AO_TOGGLE
Vector[3:0]
This attribute specifies which auxiliary outputs are in toggle mode. An
auxiliary output in toggle mode is inverted when its associated AO bit is
set in the PHY control word after the CMD_OFFSET has expired.
Table 1-59:
Auxiliary Output Attributes
(Cont’d)
Attribute
Type
Description