USB转串口芯片, USB转双串口芯片, RMB1.4, 最高波特率10M bps, 支持自动停电/上电烧录

神*** · 发表于 2024-6-28 14:21:16

RS485自动收发切换

截图202406281420055104.jpg

xxkj*** · 发表于 2024-7-4 11:20:18

现在兑换区有8引脚的STC8H2K12U了，拿来做转串口，真的很好！

jm*** · 发表于 2024-7-7 07:46:32

本帖最后由 jmg 于 2024-7-8 09:41 编辑

神*** 发表于 2024-6-28 14:21
RS485自动收发切换

This PNP auto direction change works quite well, and is simple.
It should be checked with the RS485 IC chosen, as there are caveats :

a) TX Enable (PNP turning ON) needs to be fast enough to not distort the bit-timing.
b) RX Enable (PNP turning OFF) needs to be slow enough to allow the BUS driver to change before the RX enable, otherwise you get a RXD glitch.

A PNP driver works well because it has skewed ON and OFF times. (NPN skews the wrong way)
LTspice has FAST (20MBd) RS485 LTC2862-1 and SLOW (250kBd) RS485 LTC2862-2 models so you can check the effect in LTSpice.

Digital Transistors (eg DTA014T) include the 10k base resistor, and simulates Trelease = 1.234us Tenable = 47.4ns, which is enough for up to 1-2 MBd region.

For very high baud rates, (3~11.25Mbd+) the base resistor value can drop, or you can switch to a low capacitance PMOS part like BSS84, or a Analog Sw like x3157, or Logic Gate like x1G125, can emulate a Low-C PMOS.