TTL Connector for Linksys AC Series Routers

The ONLY TTL Adapter that should be purchased for use with a Linksys AC Series Router (AKA WRT Series) is one based on an FTDI chipset.

And the Serial Header Pin Out chart / diagram in the OpenWRT documentation on the OpenWRT site is incorrect.

Summary

TTL and Serial / COM (AKA RS-232)

A good explanation of Serial Communication along with a comparison between TTL and RS-232 is here:

The Real Pin # 1

The Issue

The diagram(s) referenced and reused by many, many people for the TTL connector on the Linksys AC Series routers is incorrectly labeled. The numbering of the pins is reversed. Specifically, the numbering showing the pins labeled as 1 through 6, left to right, as looking at the board from the top / front. It should be numbered 6 through 1. Although, the perspective of the diagram could be looking from the top / rear of the board, which would make the numbering correct.

Justification

Many website tutorials, YouTube videos, diagrams, and even images on the OpenWRT website show the TTL Serial Port for the AC series of routers numbered from left to right, starting with "pin 1", as viewed from the top / front of the circuit board. This is NOT correct, although both the names / labels of the pins and what their function is (Ground, TX (Transmit), and RX (Receive)), are correct. It is an industry standard to identify "Pin 1" on a circuit board in several manners. The most common methods includes a triangle printed on the circuit board closest to "Pin 1" and a square solder connection (as viewed from the bottom). Another convention that is typically followed, but is not an absolute rule, is putting "Pin 1" closest to the nearest edge of a circuit board. The AC Series of routers all have a square solder connection on the bottom and a triangle printed on top of the circuit board for "Pin 1" on the right side of the connector, as viewed from the top. Since there is no pin out standard for that type of connector, the manufacturer (Linksys in this case) gets to define where "Pin 1" is located. And per the triangle marking, pin closest to edge, and square solder connection pin number one is located as indicated by the below image. PERIOD.

Respit

This is not intended to be any sort of attack on the nice people who have done all of the difficult work to figure things out, document it, etc. Somewhere along the way, someone made an innocent mistake, and it has been propagated quite a bit. This short diatribe on the Pin # 1 subject is intended to point out the issue in the hope that it may one day be corrected. It's also an interesting lesson in how once incorrect information gets out there, it's difficult to correct.