When data is present on the receive buffer, the MCU reads the first byte (the 'Command' byte) and switches execution based on its value. Simultaneously, the RXF# line on the FT245BM is polled for data present in the receive buffer. The MCU then enters a continuous loop, reading the CCD temperature and displaying the result on the LCD monitor. On system reset, the ATMega128 MCU clears the receiver buffer on the USB FIFO. The Windows Pyxis drivers receive data in 4096 byte chunks. The software drivers are also very simple to use, hiding most of the details involved with the USB transactions from the user.

The SND/WUP line can be toggled high to force the data in the transmit buffer to be sent to the PC on the next data-in request, regardless of how many bytes remain in the FIFO. When the TXE# line is high, the transmit FIFO is full or busy storing the last byte read. Data is placed into the transmit buffer when the WR line goes low. When the RXF# line is low, at least 1 unread byte is present in the read buffer. Data is read from the FT245BM read buffer by pulling the RD# line low when RD# is high, the data pins are placed in a high-impedance state. The FT245BM chip and software drivers provide a very simple USB interface between most PC platforms (mac, linux and windows) and a custom local 8-bit bus.

The ATMega128 AVR micro controller software communicates with the FT245BM USB parallel FIFO chip to provide control of the CCD and telescope peripherals from the PC.

Pyxis Software Version 2.10 released May 10, 2007.

Codevision avr software