usb转485电路，rx引脚的空闲电平为低

2839835353

做了一个usb转485电路，rx空闲电平不是应该为高电平吗，实测为低电平，接收数据不正确，请各位看看，哪里有问题，谢谢

renxiangbing1

A接上拉电阻，B接下拉电阻

超級狗

2839835353 发表于 2019-12-17 17:33
VCCIO接到3.3V/5V，截图没有截到

* F' z; r# M" M! `- X6 }VCCIO
- d3 I! Z# F' w, G7 ]) n: \' t+1.8V to +5.25V supply to the UART Interface and CBUS group pins (1...3, 5, 6, 9...14, 22, 23). In USB bus powered designs connect this pin to 3V3OUT pin to drive out at +3.3V levels, or connect to VCC to drive out at 5V CMOS level. This pin can also be supplied with an external +1.8V to +2.8V supply in order to drive outputs at lower levels. It should be noted that in this case this supply should originate from the same source as the supply to VCC. This means that in bus powered designs a regulator which is supplied by the +5V on the USB bus should be used.
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; ?" |' C* u& {0 j* Y0 U不清楚你有沒有照著做，只能提醒你注意這一點！


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2839835353

FT232端，RX引脚空闲状态为高电平，MAX485芯片，空闲状态为低电平，两个芯片一连接，把FT232的引脚也拉低了，呈现出RX引脚为低电平状态，也换过MAX485芯片，一样的问题，不知道问题出在哪

2839835353

485引脚接上拉电阻，用示波器看，空闲状态还是低电平。电压为0

2839835353

VCCIO接到3.3V/5V，截图没有截到
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wangfayang888

你RS485_A和RS485_B 线序接错了啊

hyz12888

;P

sunny哥

好像是这么回事、485A/B序接反了

qiantan

试试6#楼说的，先把R12、R13去掉，线序换下

Bill168

:):):):)

Ankky

悬空应该是高电平才对啊。

2839835353

超級狗 发表于 2019-12-17 18:12
( ^, O5 @+ ^& ]7 lVCCIO
+1.8V to +5.25V supply to the UART Interface and CBUS group pins (1...3, 5, 6, 9...14, 22,  ...

感谢指正:lol:lol

2839835353

wangfayang888 发表于 2019-12-17 18:16
你RS485_A和RS485_B 线序接错了啊

感谢指正，AB的上下拉接反了

2839835353

sunny哥 发表于 2019-12-18 08:30
好像是这么回事、485A/B序接反了

感谢指正，AB的上下拉接反了