USB to RS232 Converter Circuit Description

For the complete equipment needed to make schema PC via a USB connection to RS232 converter
We scan controller is an independent board that communicates with the PC via USB connection. This encourages galvos XY scanner and generate signals for data acquisition time.
USB to RS232 converter board is a PIC microcontroller-based device that receives signals from a PC USB and change the signal to an RS232 output. Output signal can be sent to one of the three serial ports. Device that can be connected to the RS232 port, including XY

The USB to RS232 Converter board is a PIC microcontroller based device that receives a USB signal from a PC and converts the signal to an RS232 output.  The output signal can be sent to any one of three serial ports.  Devices which may be connected to the RS232 ports include the ASI Inc. X-Y Stage, the Olympus Z-Focus, and the Mai Tai LASER


The circuit has two power options available.  When the 0Ω Resistor noted above in Figure 1 is in place, the circuit will draw power from the USB +5V line.  When the resistor is absent, power is provided via a 2 pin connector, and an AS78L 5V positive voltage regulator is used. This board uses a PIC18F4455 to receive USB commands which are converted to RS232 protocol via a DS275 Line-Powered Transceiver Chip.  There is one transceiver chip associated with each RS232 port.  This chip’s transmitter draws power from the receive line, so an external power source is not needed to drive the transmitter line at RS232 levels.

RS-232 Settings

The default settings for RS-232 communication are set to 9600 baud, 8 bits, no parity, and no software handshaking.  Only the Transmit (TX), Receive (RX), and Ground signals are used.  The Request to Send (RTS) and Clear to Send (CTS) signals are tied together at the board level so that devices requiring the CTS signal will always be enabled to send data.  This works because the device will set its own RTS signal high, so connecting these two signals will ensure that CTS will be held high as long as the device is connected.  If an attached device requires settings different from the board default, this can be changed in the software with the exception that this board does not accommodate devices that require handshaking beyond the CTS signal.

Each device uses its own unique command set which is described in the device’s user manual or specification document.  The purpose of this board is to pass this command on to the device without modification.  The data received via USB will contain this command as well as a three-byte precursor that indicates how the command should be processed.  The first byte will be an ASCII character ‘1’, ‘2’, or ‘3’ to designate the number of the port that the command is intended for.  The next two bytes will be a two-character ASCII code which indicates the type of device connected to this port.  This allows the embedded software to change any settings for that particular device if necessary.  It also enables the host to keep track of the commands sent to each device.  The ASCII command to be sent to the device follows.  Each device may require a “terminator” to indicate the end of the command such as a carriage return, line feed, or combination of the two.