In addition, if the board will be enclosed in a box, the two pin connector in parallel with the Setup pushbutton will come handy to connect a panel mount one. External connections are the B-type USB female socket and the GPIB female socket. The FT232R, which is the only SMT component, is mounted at the copper side of the PCB. Herebelow the drawing of the PCB layout and the close-up pictures of a mounted unit:
More details about Setup mode can be found in the USE AND OPERATION section. Normal operation is restored at the end of Setup procedure, or unplugging-replugging the interface from the host PC. Even if the GPIB cable can be left connected to the instrument, in Setup mode the GPIB port is not monitored by the Pic-Plot2.
In this mode the PC is used to read/change a few set-and-forget parameters that are stored in the non-volatile memory of the microcontroller. Two LEDs (LD1-green, LD2-red) respectively indicate:Ī small pushbutton switch is provided to enter Setup mode. See also COUNTER CIRCUITS JALV2 PIC16F628 There is no power switch: the interface is ON whenever plugged to the host PC. A standard A-B USB cable is needed for data and power connection. Then the FT232 manages the USB communication to the host PC where a Virtual COM Port (VCP) has been created by installing the proper drivers. Once the device is addressed and it receives data from the Talker, the same data are forwarded from microcontroller UART to the FT232 at 38400 baud. Controller mode is not needed for the intended functionality, and therefore is not supported. The microcontroller does all the necessary jobs to emulate GPIB Device functionality, in both Listener and Talker mode, by recognizing addressing, commands and managing the Handshake lines. No oscillator crystal is needed because the FT232 provides the 12 MHz clock for the microcontroller, and the 5V needed to supply the whole circuit are taken from the USB host PC. The microcontroller manages the GPIB protocol and signals, while the FT232 does the bridging between the USB and the microcontroller UART. It features an 8-position DIP switch to set the data rate from 300 bps all the way up to 38.4 kbps -with six data rates in between It also senses if the serial device is DTE or DCE and adjusts accordingly. The hardware of Pic-Plot2 interface is quite simple: the active components are a Microchip PIC16F628 microcontroller and an FT232 chip from FTDI. The Black Box Parallel to Serial Converter IV is ideal for connections to an HP JetDirect parallel print server.
PARTS AND KIT AVAILABILITY SCHEMATIC AND DETAILS SOFTWARE USE AND OPERATION VERIFIED GPIB INSTRUMENTS It is based on a PIC16F628 microcontroller and an FT232R chip. The operation of this interface is not just limited to digital plotter emulation: any data intended to be received by a GPIB Device (addressable or listener only) can be captured from the instrument and brought out to the USB port, including raw measurement arrays or rasterized data for a graphic printer. Power is taken from the USB port to simplify cabling and get rid of a DC adaptor. GPIB addresses and other set-and-forget parameters can be configured by a simple Setup menu, then no Dip-switches are used. It emulates the HP7470A operation on the GPIB side, and outputs the HP-GL data at the USB port to be read and stored on the PC by any capturing software. Pic-plot now goes to USB! A perfect low cost solution to quickly get screen plots of your GPIB instrument on your laptop PC without complex software.