Architecture
LatticeECP/EC Family Data Sheet
Lattice Semiconductor
Polarity Control Logic
In a typical DDR Memory interface design, the phase relation between the incoming delayed DQS strobe and the
internal system Clock (during the READ cycle) is unknown.
The LatticeECP/EC family contains dedicated circuits to transfer data between these domains. To prevent setup
and hold violations at the domain transfer between DQS (delayed) and the system Clock a clock polarity selector is
used. This changes the edge on which the data is registered in the synchronizing registers in the input register
block. This requires evaluation at the start of each READ cycle for the correct clock polarity.
Prior to the READ operation in DDR memories DQS is in tristate (pulled by termination). The DDR memory device
drives DQS low at the start of the preamble state. A dedicated circuit detects this transition. This signal is used to
control the polarity of the clock to the synchronizing registers.
sysI/O Buffer
Each I/O is associated with a flexible buffer referred to as a sysI/O buffer. These buffers are arranged around the
periphery of the device in eight groups referred to as Banks. The sysI/O buffers allow users to implement the wide
variety of standards that are found in today’s systems including LVCMOS, SSTL, HSTL, LVDS and LVPECL.
sysI/O Buffer Banks
LatticeECP/EC devices have eight sysI/O buffer banks; each is capable of supporting multiple I/O standards. Each
sysI/O bank has its own I/O supply voltage (V
), and two voltage references V
and V
resources allow-
CCIO
REF1
REF2
ing each bank to be completely independent from each other. Figure 2-34 shows the eight banks and their associ-
ated supplies.
In the LatticeECP/EC devices, single-ended output buffers and ratioed input buffers (LVTTL, LVCMOS, PCI and PCI-
X) are powered using V
LVTTL, LVCMOS33, LVCMOS25 and LVCMOS12 can also be set as fixed threshold
CCIO.
input independent of V
In addition to the bank V
supplies, the LatticeECP/EC devices have a V core logic
CCIO.
CCIO CC
power supply, and a V
supply that power all differential and referenced buffers.
CCAUX
Each bank can support up to two separate VREF voltages, VREF1 and VREF2 that set the threshold for the refer-
enced input buffers. In the LatticeECP/EC devices, some dedicated I/O pins in a bank can be configured to be a
reference voltage supply pin. Each I/O is individually configurable based on the bank’s supply and reference volt-
ages.
2-28
LATTICE [ LATTICE SEMICONDUCTOR ]
