Differential ports¶
The RJ45 jacks labelled with port ranges (9-12, 17-20, 21-24, …) are
differential pixel ports. Each carries four pixel strings as balanced
(RS-422-style) data over a standard network cable. At the far end, a
differential receiver turns the data back into four ordinary pixel outputs and powers
them from its own supply.
Differential data travels hundreds of feet. Use it to put pixel outputs where the props are, instead of running long pixel leads from the controller.
These are not Ethernet ports
Do not plug the differential ports into a network switch, router or PC. The controller's one real Ethernet port is the metal-shielded jack with built-in LEDs. The differential jacks are all black plastic.
Pinout¶
All differential ports on all boards use the same pinout. The four strings are called
A–D in the order of the label. On a jack labelled 17-20, A is string 17 and D is string 20.
| RJ45 pin | Signal | Cable pair (T568B colours) |
|---|---|---|
| 1 | String A + | orange-white |
| 2 | String A − | orange |
| 3 | String B + | green-white |
| 6 | String B − | green |
| 5 | String C + | blue-white |
| 4 | String C − | blue |
| 7 | String D + | brown-white |
| 8 | String D − | brown |
There is no ground and no power on the cable; all eight wires are data.
Receivers¶
Any receiver that uses the standard four-strings-per-RJ45 differential pinout above will work. That includes the Kulp Lights receivers and Falcon-compatible receivers.
- Smart Receiver SRx1: 4 strings.
- Long-range SRx2 and SRx4.
Smart receivers and chaining¶
Smart receivers can be chained: up to six receivers on one differential port, sharing that port's pixel allocation. Give each receiver in the chain its own position on its selector dial, as described in the receiver's instructions, and turn termination on at the last receiver only. Set the chain up in FPP on the port's row in the Pixel Strings table. See the FPP manual.
Pixel budget with smart receivers¶
FPP drives up to 800 pixels per port at 40 fps. The smart-receiver protocol shares that time with the pixels, so it lowers the budget. How much depends on which protocol the receivers use (set per port in FPP):
| Protocol | Overhead | Does 800 px at 40 fps fit? |
|---|---|---|
| None (dumb receivers) | none | Yes |
| v1 | about 12 / 36 / 66 px for 1 / 2 / 3 receivers, every frame | With 1 receiver only. 3 receivers leave about 757 px. |
| v2 | none for the first receiver, then about 3–4 px for each one after | Yes, up to the 6-receiver maximum (about 17 px for 6) |
| V4 | a config packet of about 25 px on 1 frame in 12 | Just: about 798 px is the safe limit |
| V5 | a status query of up to about 96 px on most frames | No. Keep to about 725 px, or run 800 px at about 36–37 fps |
The budget is per port. All the receivers in a chain share it: output 1 of receivers 1, 2 and 3 together get what's left on that port. An empty receiver position in the middle of a v1/v2 chain also costs one pixel.
V5 costs the most because it is the protocol that reports back (see below): on most frames the controller sends a query and then waits for the receiver to answer. If you don't need the readings, V4 costs far less.
Two-way ports (Pro and Max boards)¶
On the K8-Pro, K8-Max, K16-Pro, K16-Max, K32-Pro and K32-Max the differential ports are bi-directional. Pair 1/2 also carries data back from the receiver. Falcon V5 smart receivers use it to report their eFuse status, current and other readings, and FPP shows them on the Port Status page next to the local ports. Only Falcon V5 receivers report back. Every other receiver works as a normal, send-only receiver on these ports.
On the K16, K32, K8-PB and K40D-PB the differential ports are send-only. Every receiver works, but none can report back.
K8-PB and K40D-PB: no V5
FPP drives the K8-PB and K40D-PB with its BBB48String output, which has no V5 protocol. Set smart receivers on these boards to v1, v2 or V4. A V5 setting falls back to V4.
Cabling tips¶
- Use solid-core Cat5e or Cat6 with factory-made or carefully crimped ends. A bad crimp on one pair kills one string and is hard to find.
- Outdoors, use outdoor-rated (UV/direct-burial) cable and keep the RJ45 ends dry.
- If a receiver has a terminator setting, turn termination on at the last receiver in a chain only.
- Each receiver has a test button and data LEDs. Use them to tell a cable problem from a configuration problem. See the receiver's documentation.