3-10
DC and Switching Characteristics
Lattice Semiconductor LatticeECP/EC Family Data Sheet
RSDS
The LatticeECP/EC devices suppor t differential RSDS standard. This standard is emulated using complementary
LVCMOS outputs in conjunction with a parallel resistor across the driver outputs. The scheme shown in Figure 3-3
is one possible solution for RSDS standard implementation. Use LVDS25E mode with suggested resistors for
RSDS operation. Resistor values in Figure 3-3 are industry standard values for 1% resistors.
Figure 3-3. RSDS (Reduced Swing Differential Standard)
Table 3-3. RSDS DC Conditions
5V Tolerant Input Buffer
The input buffers of the LatticeECP/EC family of devices can support 5V signals by using a PCI Clamp and an
external series resistor as shown in Figure 3-4.
Figure 3-4. 5 V Tolerant Input Buffer
Parameter Description Typical Units
Z
OUT
Output impedance 20 ohm
R
S
Driver series resistor 294 ohm
R
P
Driver parallel resistor 121 ohm
R
T
Receiver termination 100 ohm
V
OH
Output high voltage 1.35 V
V
OL
Output low voltage 1.15 V
V
OD
Output differential voltage 0.20 V
V
CM
Output common mode voltage 1.25 V
Z
BACK
Back impedance 101.5 ohm
I
DC
DC output current 3.66 mA
100
294
294
On-chip
Emulated
RSDS Buffer
VCCIO = 2.5V
VCCIO = 2.5V
Zo = 100
+
-
121
Off-chip
External
Resistor
5V Signals from
Legacy Systems
V
CCIO
