Ch340 Datasheet (I) 1 usb to Serial Port Chip ch340

CH340 Datasheet (I)
5 
For CH340X and CH340C/N whose last 3-digit batch number is greater than B40, IO supports 5V, avoiding 
inward current poured backwards. 
CH340K not only avoids inward current poured backwards, but also reduces drive capacity to external, 
avoiding current poured backwards from CH340 to external.
CH340 supports USB device suspending automatically to save power. USB device suspending is forbidden 
when NOS# is driven low. 
DTR# pin of CH340G/C/T/K is used as a configuration input pin before the USB configuration completion. 
An external 4.7K
Ω
pull-down resistor can be connected with this pin to generate default low during USB 
enumeration, to apply larger supply current from USB bus via the configuration descriptor. 
CH340 has integrated USB pull-up resistor, UD+ and UD- pins should be connected to USB bus directly. 
In serial UART mode, CH340 contains these pins: data transfer pins, MODEM interface signals and 
assistant pins. 
Data transfer pins contain: TXD and RXD. RXD keeps high when UART reception is idle. For 
CH340G/C/T/R, if the R232 pin is driven high, assistant RS232 function will be enabled, an internal inverter 
will automatically insert to the RXD, and the pin becomes low by default. When UART transmission is idle, 
the TXD of CH340G/C/N/E/X/B/T keeps high, CH340K is weak high, while CH340R keeps low. 
MODEM interface signals contain: CTS#, DSR#, RI#, DCD#, DTR# and RTS#, CH340C also provides 
OUT# pin. All these MODEM interface signals are controlled and function defined by computer 
applications. 
Assistant pins contain: IR#, R232, CK0, ACT# and TNOW. When IR# is low, infrared serial interface mode 
is enabled. R232 is used to control assistant RS232 function. If R232 is driven high, the RXD input will be 
reversed automatically. ACT# is USB device configuration complete status output (such as USB infrared 
adapter ready). TNOW indicates CH340 is transmitting data from UART when it is high and becomes low 
when transmits over. In RS485 and other half-duplex mode, TNOW could be used to indicate UART 
transmit-receive status. IR# and R232 are detected only once after power on reset.