The main components of the evaluation board U1 is the chip of the CH376S, but some signal named CH375 or CH374 in the picture.
Crystal X1 is standard 12MHz, USB host demands more accurate frequency, the error of the X1 demands less than 0.4‰, basically the average 12MHz crystal can meet the requirements. Strongly suggest that shorten the length of the relevant lead, in order to reduce interference.
Capacitance C4 used for internal Local power supply decoupling back to reduce EMI during the USB transmission process. Capacity is 4700pF to 0.1uF, 0.01uFcapacity of average 103 SMD is OK.
P4 is a USB port, USB HOST can be used, also can be used for USB DEVICE mode devices, resistors R1 to limit the output current to an external USB devices to avoid disk and other USB devices just insert the power supply voltage cause Short-term decline and even cause CH376 or MCU microcomputer reset or internal RAM abnormal data errors. If the USB external hard drive, then the resistor R1 should be replaced by a smaller inductor DC resistance, or another group with a 5V power supply directly to provide greater operating current (500mA or more) to the external hard drive. In addition, USB-HOST sockets in the capacity of decoupling capacitor C9 can not be too small, some large capacity (should be greater than 100μF) can be reduced the power supply voltage fluctuations when the USB device just insert.
P5 is the SD card socket, can connect the standard size SD card, and other specifications of the SD card may need to convert an additional seat. Resistor R3 is used to restrict the output current to an external SD card, to avoid the supply voltage cause short-term decline when just insert the SD card.
P1 is a signal 8-bit parallel port for connecting the microcontroller parallel port, the necessary signals of parallel port including D0-D7, A0, RD #, WR #, CS #, and GND, and the INT # is optional.
P2 is a signal SPI serial port for connecting the SPI interface of microcontroller, the necessary signals of SPI including SCS, SCK, SDI, SDO, and GND, and the INT # is optional.
P3 is asynchronous serial port for connecting the asynchronous serial of the microcontroller; the necessary signals of asynchronous serial including RXD, TXD and GND, and the INT # is optional. P3 also provides a write-protect of SD card and plug the state SDINSERT SDWP signal line.
P1, P2, P3 communication port on the above, can provides 5V power supply from internal to the evaluation board. And provide optional hardware reset signal to RSTI pin of CH376. If circuir have μP control circuit in the product, it should provide the same reset signal for CH376 and microcontroller. Note, try to shorten the length between the evaluation board and microcontroller, the longest can not more than 20cm, or need to use a signal to interval a landline special rewiring.
J3 is used to select CH376 chip voltage, the voltage is 5V when short circuit of 1-2 feet, when short circuit of 2-3 pin, voltage is 3.3V. The default is 5V, but when the MCU voltage is equal to or less than 3.3V, 3.3V voltage can be selected for the CH376. When the voltage is 5V of the CH376 chip, J2 must be disconnected, when the CH376 chip’s voltage is 3.3V, J2 must be shorted.
J1, J5 and J6 are used to power or hardware reset and select CH376 communication interface with the microcontroller:
If the J1shorted, J5 off, J6 off, then it is 8-bit parallel port;
If you J1 off, J5 shorted, J6 shorted, then it is SPI interface;
if you J1 off, J5 off, J6 off, then the asynchronous serial port.
Some example program may be debugging the state information by microcontroller’s serial output, if need to display the monitoring information, after converted the microcontroller serial though the RS232, then connected the computer and using a serial port monitor/debug tool software to check. If use CH375 evaluation board, J2 can be connected to the computer’s serial ports; if the computer has not serial or the serial has been occupied by other device, the USB serial chip CH341 can provide the simulated serial port.
CH375 evaluation board inside device under the 5V power supply must add resistance R0 and remove 3.3V voltage stabilizer D4, under the 3.3V power supply, must add stabilizer D4 and remove the resistance R0. The default is 5V power supply.