Post B35dsHqlRBxCT19mN6 by arroz@mastodon.social
 (DIR) More posts by arroz@mastodon.social
 (DIR) Post #B35dsHqlRBxCT19mN6 by arroz@mastodon.social
       2026-02-07T10:34:26Z
       
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       Ok question for #electronics and #retrocomputing folks, if I disable all sorts of hardware and software handshakes, and I wire the TXD directly to the RXD pins of a RS-232 serial port, I should see the echo of the data I'm sending, correct? And I should see the signal bouncing between >3V and <-3V on that wire?I'm starting to think the USB-serial adapter I bought is broken.
       
 (DIR) Post #B35dsJRJWmmhOfGTyq by tomjennings@tldr.nettime.org
       2026-02-07T21:09:39Z
       
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       @arroz Yes you should. Bit some serial port programs may require control signals to ne in aome particular state, though today in 2026 possibly few.
       
 (DIR) Post #B35dsMyOOG1iM7lRSK by arroz@mastodon.social
       2026-02-07T10:58:12Z
       
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       So here's what happening: the yellow line is the TXD, blue is RXD. On the first two photos, both are NOT wired together. TXD goes low, RXD goes high (weird, but maybe bias?). The signal is clearly seen going up and down the threshold, and TXD works fine. Third photo is both lines wired together (and blue probe disconnected). The signal never goes below 0V! And naturally I get no data back. Is the RXD line broken? #electronics #retrocomputing
       
 (DIR) Post #B35dsRpMLGlvPYZnZQ by arroz@mastodon.social
       2026-02-07T11:14:55Z
       
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       Mystery solved, this thing is working, but wired wrong. 😂 Thank you @barries! https://mastodon.sdf.org/@barries/116029020950642130 So now I have to wire two non-standard RS-232 ports, the FDD 3000 from 40 years ago and the new adapter, and at some point an old PowerBook with also a non-standard thing. My brain is feeling the pain already. #electronics #retrocomputing
       
 (DIR) Post #B35dsWwzIKqRIfBSee by arroz@mastodon.social
       2026-02-07T11:40:54Z
       
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       Here's the pinout of this stupid adapter:USB-serial adapter:Pin 2: DTRPin 3: TXDPin 4: RXDPin 5: Ground, I think. I hope.Pin 7: CTSPin 8: RTSPin 9: DSRWhat a lovely thing.