The DataSheet of CH340 (the first) 1 USB to serial chip CH340 English DataSheet Version: 1D The DataSheet of CH340 (the first) 2 3. Package Package shape Width of plastic Pitch of Pin Instruction of package Ordering type SSOP-20 5.30mm 209mil 0.65mm 25mil Shrink small outline package of 20-pin CH340T SSOP-20 5.30mm 209mil 0.65mm 25mil Shrink small outline package of 20-pin CH340R 4. Pins Pin Description(description in bracket is only about Pin No. Pin Name Pin Type CH340R) Positive power input port, requires an external 0.1uF 19 VCC POWER power decoupling capacitance 8 GND POWER Public ground, ground connection for USB connects of VCC to input outside power while 3.3V, 5 V3 POWER connects of 0.01uF decoupling capacitance outside while 5V Input of crystal oscillator, attachment of crystal and 9 XI IN crystal oscillator capacitance outside Opposite output of crystal oscillator, attachment of 10 XO OUT crystal and crystal oscillator capacitance outside Directly connect to D+ data wire of USB bus, set up 6 UD+ USB signal pull-up resistor internal 7 UD- USB signal Directly connect to D- data wire of USB bus Forbid USB device suspending, active with low, set up 20 NOS IN pull-up resistor internal 3 TXD OUT Serial data output(opposite phasic output of CH340R) Serial data input, set up controlled pull-up and 4 RXD IN pull-down resistor MODEM liaison input signal, clear sending, active with 11 CTS IN low(high) MODEM liaison input signal, data equipment is ready, 12 DSR IN active with low(high) MODEM liaison input signal, oscillate ring to prompt, 13 RI IN active with low(high)