CH340 Datasheet (I)
11
The figure above also shows that USB is converted to RS232. This circuit has
the same function as the
circuit shown in Section 7.2 except the range of output RS232 is narrower. When R232 pin is driven high,
the assistant RS232
function will be enabled,
just need to add some diodes,
transistors,
resistors and
capacitors, the special level converter chip U5 in Section 7.2 could be replaced
and the hardware cost is
lower.
7.4. USB to RS485 UART
TNOW pin can be used to control DE (active high and transmit enabled) and RE# (active low and receive
enabled) pins of RS485 transceiver.
7.5. USB to Infrared adapter
(figure below)
The figure below shows a USB to infrared adapter design which is composed of a USB to IrDA infrared chip
(CH340R) and an infrared transceiver U14 (ZHX1810/HSDL3000 etc). The R13 resistor is used to weaken
influence of large current in infrared transmitting. The R14 current limiting
resistor should be adjusted
according to the manufacturer
’
s recommended value of the U14 infrared transceiver.
7.6. Connect to MCU and supply power together
(figure below)
The figure above is a reference design to achieve USB connection on an MCU by connecting it to a CH340
via TTL UART. Here self-power mode is selected, VCC supports 5V or 3.3V (V3 shorted to VCC if VCC is
3.3V), and USB bus power (VBUS) is not used at all (Can be tested by connecting series resistor to I/O of
MCU if needed). CH340 shares the same power source with MCU, hence there would be no current inrush
CH340 Datasheet (I)
12
through I/O between CH340 and MCU.
Unused CH340 pins can be not connected. For CH340C/N/K/E/X/B, X6, C17 and C18 are not required.
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