I need some advice:
- i want to connect an altera FPGA to a computer by USB interface.
- i want to avoid placing an microcontroller in my board..
- i want to set a nios II to "talk" to the computer
- i only need the fpga/nios to act as slave, never as host
- the interface chip , should be inexpensive , low pincount & simple.
i know there is demo board terrasic D2-11 with ISP1362 or CY7C67200 , but this chips are as expensive as using an real stand alone microcontroller.
would it be a good idea to use a USB to spi/uart transceiver , in order to interface my NIOS to a PC?
any chip/topology recommendations?
thanks for the advice…
Best Answer
I would recommend either a USB UART chip or a USB FIFO chip. The USB UART chip will use 2 I/O pins, unless you want to add flow control on top of that. There are quite a few good USB to serial options out there. USB FIFO chips require a few more pins, generally 12 pins for 8 data and 4 flow control, but they have some advantages compared to USB UART chips. First, there is no mucking around with the baud rate. Second, they can run at a much higher speed - for example, the FT2232 is rated at 8 MBps / 64 Mbps. The FT245 is a decent solution for a USB FIFO chip, though there may be others. The FT2232 will also work, but requires a small external EEPROM so it comes up in FIFO mode. The FT2232 also has the advantage that it can speak JTAG, so you can use a one-chip solution for both communication as well as configuration of the FPGA via JTAG.