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CH340 Datasheet(PDF) 3 Page - Jiangsu Haoheng Co., Ltd.

Part No. CH340
Description  USB to serial chip
Download  6 Pages
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Maker  WCH [Jiangsu Haoheng Co., Ltd.]
Homepage  http://wch.cn/

 3 page
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The DataSheet of CH340 (the first)
MODEM liaison input signal, carrier wave detection,
active with low(high)
MODEM liaison output signal, data endpoint is ready,
active with low(high)
MODEM liaison output signal, request to send, active
with low(high)
CH340T:negative phasic clock output
(CH340R:USB configuration is finished state output,
active with low)
Assistant RS232 enable, active with high, set up
pull-down resistor internal
CH340T: unconnected, must be suspended
CH340R:Serial interface mode set input, set up pull-up
resistor internal, low level is SIR infrared serial
interface, high level is common serial interface
CH340T: clock output
CH340R:unconnected, must be suspend
5. Function description
CH340 chip set up USB pull-up resistor internal, UD+ and UD- pins must be connected to USB bus
CH340 chip set up power up reset circuit internal.
When CH340 chip is working normally, the outside must supply 12MHz clock signal to XI pin. In
generally, clock signal is generated by inverter in CH340 through oscillating of crystal keeping frequency. A
crystal of 12MHz between XI and XO, XI and XO connect a high frequency oscillator capacitance to ground
respectively can compose the peripheral circuit.
CH340 chip supports 5V and 3.3V power voltage. When using 5V source power, the VCC input 5V
power and the pin of V3 must connect with 4700pF or 0.01uF decoupling capacitance. When using 3.3V
power voltage, connects V3 with VCC, and input 3.3V power voltage. And the other circuit voltage which is
connected with CH340 is no more than 3.3V.
CH340 automatically supports USB device suspending to save power consume. NOS# is low–level can
forbid USB device suspending.
In asynchronous serial interface mode, CH340 chip contains these pins: data transfer pin, MODEM
liaison signal pin and assistant pin.
Data transfer pin contains: TXD pin and RXD pin. When serial interface is idle, RXD must be
high-level. If R232 is high-level, use assistant RS232 function, then RXD pin automatically inserts a inverter
internal, and low-level is in default. When serial interface output is free, the TXD in CH340H and CH340T
is high level, TXD in CH340R is low-level.
MODEM liaison signal pin contains: CTS#, DSR#, RI#, DCD# and RTS#. All these MODEM liaison
signal are controlled by computer application program and application program defines function.
Assistant pin contains: IR#, R232, CKOH, CKOL and ACT#. When IR# is low-level, starts infrared
serial interface mode. R232 is used to control assistant RS232 function. When R232 is high-level, RXD pin
automatically insert a inverter internal, and output opposite phase clock from CKOH and CKOL. ACT# is
USB device configuration finished state output (such as USB infrared adapter is ready) when R232 is
low-level. IR# and R232 only be detected once a time after power reset.
CH340 set separate transceiver buffer internal and supports simplex, semiduplex and full duplex
asynchronous serial communication. Serial data contains one low-level start bit , eight or nine data bit and

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