I/O Standards Support
Designing with RSDS
Cyclone II devices support the RSDS output standard using the LVDS
I/O buffer types. For transmitters, the LVDS output buffer can be used
with the external resistor network shown in Figure 11–7.
Figure 11–7. RSDS Resistor Network Note (1)
Cyclone II Device
≤ 1 inch
Resistor Network
LVDS Transmitter
RSDS Receiver
50 Ω
50 Ω
R
= 100 Ω
R
P
L
Note to Figure 11–7:
(1) RS = 120 Ωand RP = 170 Ω.
f
For more information on the RSDS I/O standard, see the RSDS
specification from the National Semiconductor web site
(www.national.com).
A resistor network is required to attenuate the LVDS output voltage
swing to meet the RSDS specifications. The resistor network values can be
modified to reduce power or improve the noise margin. The resistor
values chosen should satisfy the following equation:
R
P
R
S ×
2
=
50Ω
R
R
P
+
S
2
Additional simulations using the IBIS models should be performed to
validate that custom resistor values meet the RSDS requirements.
Single Resistor RSDS Solution
The external single resistor solution reduces the external resistor count
while still achieving the required signaling level for RSDS. To transmit
the RSDS signal, an external resistor (RP) is connected in parallel between
the two adjacent I/O pins on the board as shown in Figure 11–8. The
recommended value of the resistor RP is 100 Ω.
11–8
Cyclone II Device Handbook, Volume 1
Altera Corporation
February 2007
ALTERA [ ALTERA CORPORATION ]
