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发表于 2023-7-30 06:31:23
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本帖最后由 jmg 于 2023-7-30 09:16 编辑
Why not just buy serial cables for other chips?
PL2303 CH340 FT232R CP2102 these four chips, CP2102 does not support the use of external crystal.
Both FT232R CP2102 are expensive and rare. The price of genuine PL2303 CH340 FT232R is about the same.
Of the four chips, only PL2303 supports 12M high-frequency communication, and the others can only support 2M~3M
The crystal is not essential anymore, only old parts use crystals, or HS-USB parts.
The devices lock to the USB 1ms Frame rate, so they are good to some fraction of one percent. (~0.3% typical) that is in most cases more than good enough.
Only if you want to use the UART for other purposes, like oscillator calibrate, as STC do in their programmers, do you need a crystal.
You can test the precision of any UART, by sending a large file of 0x55 and connect a frequency counter.
PL2303 can be set to 12Mbd, but it cannot sustain that speed over FS-USB.
I tested the newest PL2303GC parts, and they can receive just under 768 bytes before they lose characters at 12MBd, and with no handshake lines enabled, they can actually only sustain just under 3MBd streams.
ie their 12Mbd banner value, is largely an illusion, with many caveats.
The new versions of these chips to look for are
PL2303TA -> PL2303Gx
CP2102 -> CP2102N
CH340 -> CH343, CH9102, CH9101
and if you are worried about crystals and baud speeds, more HS-USB options are now available
CH347 -> new TSSOP20 HS-USB UART
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