Ja header on Arty board

(Thinh) #1

Hello, I’ve been wonder that’s the use of the ja header on Arty board? For the last few days I’ve been mistaking it with “normal” GPIO. Now that I know that it’s not the GPIO output, then what’s the use of it? It seems to be always remain floating no matter what I do. Thanks in advance.

(Donnie Agema) #2

10 Pmod Connectors

Pmod connectors are 2×6, right-angle, 100-mil spaced female connectors that mate with standard 2×6 pin headers. Each 12-pin Pmod connector provides two 3.3V VCC signals (pins 6 and 12), two Ground signals (pins 5 and 11), and eight logic signals, as shown in Fig. 16. The VCC and Ground pins can deliver up to 1A of current, but care must be taken not to exceed any of the power budgets of the onboard regulators or the external power supply (these are described in the “Power supplies” section).

Digilent produces a large collection of Pmod accessory boards that can attach to the Pmod expansion connectors to add ready-made functions like A/D’s, D/A’s, motor drivers, sensors, and other functions. See www.digilentinc.com for more information.

The Arty has four Pmod connectors, some of which behave differently than others. Each Pmod connector falls into one of two categories: standard or high-speed. Table 4 specifies which category each Pmod falls into, and also lists the FPGA pins they are connected to. The following sections describe the different types of Pmods.

Figure 10.1. Pmod connector.

Pmod JA Pmod JB Pmod JC Pmod JD
Pmod Type Standard High-Speed High-Speed Standard
Pin 1 G13 E15 U12 D4
Pin 2 B11 E16 V12 D3
Pin 3 A11 D15 V10 F4
Pin 4 D12 C15 V11 F3
Pin 7 D13 J17 U14 E2
Pin 8 B18 J18 V14 D2
Pin 9 A18 K15 T13 H2
Pin 10 K16 J15 U13 G2

10.1 Standard Pmod

The standard Pmod connectors are connected to the FPGA via 200 Ohm series resistors. The series resistors prevent short circuits that can occur if the user accidentally drives a signal that is supposed to be used as an input. The downside to this added protection is that these resistors can limit the maximum switching speed of the data signals. If the Pmod being used does not require high-speed access, then the standard Pmod connector should be used to help prevent damage to the devices.

10.2 High-Speed Pmod

The High-speed Pmods use the standard Pmod connector, but have their data signals routed as impedance matched differential pairs for maximum switching speeds. They have pads for loading resistors for added protection, but the Arty ships with these loaded as 0-Ohm shunts. With the series resistors shunted, these Pmods offer no protection against short circuits, but allow for much faster switching speeds. The signals are paired to the adjacent signals in the same row: pins 1 and 2, pins 3 and 4, pins 7 and 8, and pins 9 and 10.

Traces are routed 100 ohm (+/- 10%) differential.

These connectors should be used only when high speed differential signaling is required or the other Pmods are all occupied. If used as single-ended, coupled pairs may have significant crosstalk. In applications where this is a concern, the standard Pmod connector shall be used. Another option would be to ground one of the signals (drive it low from the FPGA) and use its pair for the signal-ended signal.

Since the High-Speed Pmods have 0-ohm shunts instead of protection resistors, the operator must take precaution to ensure that they do not cause any shorts.

Source: https://reference.digilentinc.com/reference/programmable-logic/arty/reference-manual?redirect=1

(Thinh) #3

Thank you for the reply. I’ve read that info however. I do know that it’s a “Standard Pmod” on the Arty board. What I’m trying to ask is the use of it in FE300 evaluation source code. I’ve seen that it is attached somewhere in the source code, but did not know what it does (in the design).