Inside the programming cable, the two plugs are wired to a (often a Prolific PL2303 or CH340 chip):
as follows (tab up, pins left to right):
For (no firmware flashing), you only need three pins :
The DIY process can sometimes lead to issues. Here are the most common problems and solutions: qyt kt8900 programming cable pinout top
Ensure your TTL adapter jumper is set to 3.3V . While the KT-8900 can often tolerate 5V TTL logic, 3.3V is safer and prevents long-term degradation of the radio's processor interface.
Select the correct COM port and baud rate ( 1920019200 are common for QYT).
If you want to construct a reliable cable, you can skip the cheap, problematic clone cables and use an authoritative USB-to-TTL adapter board. Required Components Inside the programming cable, the two plugs are
But here’s where 90% of the confusion happens:
If your computer does not have a serial port, you will need a DB-9 to USB converter. The following is a common pinout for a DB-9 to USB converter:
A straight or crossover Ethernet cable will not work. The voltages are wrong, and Ethernet uses differential pairs (TX+/TX-), not single-ended TTL. Select the correct COM port and baud rate
interfaces via a 3.5mm "DATA" jack located strictly on the rear panel of the chassis.
: TXD (Transmit Data) — Sends data out from the radio to the PC.
Before diving into the pin numbers, let’s clarify the "top" reference. The QYT KT8900 uses an connector for programming, identical to an Ethernet plug. However, unlike network cables, the pinout is not T568A or T568B.