Answer: The CH340E is the 10-pin MSOP member of the CH340 family (3.0 mm body, 0.5 mm pitch). It has a built-in clock, but it brings out only TXD, RXD, RTS#, CTS# and TNOW. There is no DTR#, and no DSR#, RI# or DCD#, so Arduino-style auto-reset must be wired to RTS#. It is rated −20 to 70 °C with <1.8 % TX baud error. (WCH CH340DS1 V3D, pp.2–9.)
Key specifications
| Parameter | Value | Condition | Source |
|---|---|---|---|
| Package | MSOP-10, 3.0 mm body, 0.50 mm pitch | — | §3, p.2 |
| Pinout | 1 UD+, 2 UD−, 3 GND, 4 RTS#, 5 CTS#, 6 TNOW, 7 VCC, 8 TXD, 9 RXD, 10 V3 | — | Pin diagram, p.2 |
| Modem signals | RTS#, CTS# only (no DTR#, DSR#, RI#, DCD#) | — | p.2 |
| TNOW | High while transmitting, low when done | RS485 direction control | §5.1 p.6; §7.4 p.13 |
| Supply, 5 V mode | 4.0 / 5 / 5.3 V; 7 typ / 20 max mA | V3 to 0.1 µF | §6.2, p.8 |
| Supply, 3.3 V mode | 3.1 / 3.3 / 3.6 V; 4 typ / 12 max mA | V3 tied to VCC | §6.3, p.9 |
| USB suspend current | 0.05 typ / 0.15 max mA (5 V) | — | §6.2, p.8 |
| TX baud-rate error | < 1.8 % | — | §5.4, p.7 |
| Internal clock error | ±1.2 % (−5 to 55 °C); ±1.8 % (−25 to 75 °C) | Max | §6.4, p.9 |
| Ambient temperature | −20 to 70 °C | Operating | §6.1, p.8 |
Pinout (MSOP-10)
| Pin | Name | Notes |
|---|---|---|
| 1 / 2 | UD+ / UD− | Straight to the USB connector |
| 3 | GND | — |
| 4 | RTS# | Modem output, active low; use it for auto-reset |
| 5 | CTS# | Modem input, active low |
| 6 | TNOW | High while the UART is sending |
| 7 | VCC | 0.1 µF decoupling |
| 8 | TXD | Idles high |
| 9 | RXD | Keep high when idle |
| 10 | V3 | 5 V: 0.1 µF · 3.3 V: tie to VCC |
Auto-reset without DTR#
Most Arduino-style boards reset the MCU from DTR# through a 100 nF capacitor. On CH340E, wire that capacitor to RTS# (pin 4) instead. Upload tools that toggle both DTR and RTS will still pulse the reset line. Tools that toggle only DTR won’t, so check your toolchain’s reset method.
If you need DTR# in a 10-pin MSOP, the same datasheet lists CH340X: its pin 6 can be switched from TNOW to DTR# with an external resistor (§5.3). That is a different part number; we have no page for it yet.
RS485 with TNOW
TNOW goes high while the CH340E is sending and returns low when the frame is done (§5.1). Tie it to an RS485 transceiver’s DE and RE# pins to switch direction automatically, with no firmware timing (§7.4).
Pitfalls specific to CH340E
- Expecting DTR# on CH340E. It has none; auto-reset must use RTS#.
- Hand-soldering MSOP-10 at 0.5 mm pitch on a footprint drawn for SOP. Use the MSOP land pattern.
- Wiring a 5 V-powered CH340E’s TXD straight into a 3.3 V-only MCU pin. Output high is at least VCC − 0.6 V, so about 4.4 V or more (§6.2). Power it from 3.3 V instead. CH340X, not CH340E, adds 5 V-tolerant I/O at 3.3 V.
- Putting it in a −30 °C enclosure. −20 °C is the lower limit.
Part numbers (information only)
CH340E (MSOP-10). Same package: CH340X (adds 5 V-tolerant I/O at 3.3 V and an optional DTR# on pin 6). WCH lists no packing suffix.
FAQ
- Does CH340E have a DTR pin? No. It has RTS# and CTS# only, so use RTS# for auto-reset.
- What is TNOW on CH340E? A transmit-active output, high while sending, used to switch an RS485 transceiver.
- Does CH340E need a crystal? No, it has a built-in clock.
- Can CH340E run at 3.3 V? Yes, from 3.1 to 3.6 V with V3 tied to VCC.
- What is the difference between CH340E and CH340X? Same MSOP-10 package; CH340X adds 5 V-tolerant I/O at 3.3 V and can turn pin 6 into DTR#.
Related (internal links)
Sources (retrieved 2026-10-26)
- WCH, USB to Serial Port chip CH340 Datasheet (CH340DS1), Version 3D: PDF https://www.wch-ic.com/download/file?id=79 ; download page https://www.wch-ic.com/downloads/CH340DS1_PDF.html (page numbers are the printed page footers).
Disclaimer
Values are copied from WCH CH340DS1 Version 3D, read on 26 Oct 2026. Upload-tool reset behaviour varies; test on your board.
Reviewed by: Jasper · Updated: 2026-10-26