Information

Nexys Video™ FPGA Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
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Page 20 of 28
The Nexys Video features four Pmod connectors of different "styles" with subtle differences between them. Table
9 summarizes these differences.
Pmod
connector
Power Analog/Digital Routing
Series
protection
Recommended usage
JXADC V
ADJ
Dual
Differential; Pairs:
1-7,2-8,3-8,4-10
100 ohm
Analog inputs; LVDS_25
input/output (V
ADJ
=2.5V)
JA
3.3 V
Digital-only
Single-ended
200 ohm
<10 MHz, LVCMOS33
JB, JC 3.3 V Digital-only
Differential; Pairs:
1-2,3-4,7-8,9-10
0 ohm
>=10MHz; LVDS_25 input only,
or TMDS_33 input/output
Table 9. Pmod differences.
JXADC is a dual digital/analog Pmod wired to auxiliary analog FPGA input pins (see description below). JA, JB, and
JC are digital-only but routed in a different manner. JA signal traces are routed as single-ended signals with no
length matching or characteristic impedance guarantees. JB and JC connector signals, on the other hand, are
routed differentially in pairs at 100 ohm characteristic impedance. Inter-pair matching is +- 20mm. The series
resistor on these two Pmods are replaced by 0 ohm shunts, so care must be exercised not to use voltages higher
than 3.3V, or short FPGA-driven pins.
For slow, single-ended digital signals below 10 MHz, all Pmod connectors are equivalent, assuming V
ADJ
is set to 3.3
V (see the Power Supplies section). For higher frequencies, the routing and series protection need to be taken into
account as well.
PMOD Pinouts
JA1: AB22
JB1: V9
JC1: Y6
JXADC1: J14
JA2: AB21
JB2: V8
JC2: AA6
JXADC2: H13
JA3: AB20
JB3: V7
JC3: AA8
JXADC3: G15
JA4: AB18
JB4: W7
JC4: AB8
JXADC4: J15
JA7: Y21 JB7: W9 JC7: R6
JXADC7: H14
JA8: AA21 JB8: Y9 JC8: T6
JXADC8: G13
JA9: AA20
JB9: Y8
JC9: AB7
JXADC9: G16
JA10: AA18
JB10: Y7
JC10: AB6
JXADC10: H15
Table 10. Nexys Video Pmod pin assignments.
Digilent produces a large collection of Pmod accessory boards that can attach to the Pmod expansion connectors
to add ready-made functions like A/Ds, D/As, motor drivers, sensors, and other functions. Visit Digilent's website
and check out the Pmod category for more information.
10.1 Dual Analog/Digital Pmod
The on-board Pmod expansion connector labeled "JXADC" is wired to the auxiliary analog input pins of the FPGA.
Depending on the configuration, this connector can be used to input differential analog signals to the analog-to-
digital converter inside the Artix-7 (XADC). Any or all pairs in the connector can be configured either as analog
input or digital input-output.
The Dual Analog/Digital Pmod on the Nexys Video differs from the rest in the routing of its traces. The eight data
signals are grouped into four pairs, with the pairs routed closely coupled for better analog noise immunity.