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Altera_Forum's avatar
Altera_Forum
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17 years ago

HSMC Interface - Signaling at 3.3V

Well, I need to connect to a CAN Transceiver. Therefor 2.5V are too less and so I need to have 3.3V for signaling(RX and TX).

I set already under [Assignments -> Device ->Device and Pin Options -> Voltage] the default I/O Voltage to 3.3V.

I also set under [Assignment -> Pins] and then [View -> Show -> Show I/O Banks] following stuff: I click on IOBANK_5A (and on IOBANK_5B) and set I/O bank VCCIO to 3.3V. This should be the VCCIO Pin assignment to 3.3V, or?

Well anyway. When I upload it(not flashing) nothing happens at the HSCM Ports(The connection form the fpga to the Interface works. Can set it to 0 or 1(2.5V)).

If I set under [Assignments -> Device ->Device and Pin Options -> Configuration] Configuration device I/O voltage 3.3V it doesnt help too.

If I activate the "Force VCCIO to be compatible with configuration I/O voltage" at [Assignments -> Device ->Device and Pin Options -> Configuration] Quartus doesnt get the place and route.

I use Quartus 9.0 and a Stratix III board.

How can I drive the voltage level to 3.3V at the HSMC Interface(Banks 5A,5C and 6A,6C).

I am getting insane. Pls help :)

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    17 years ago

    You are ignoring a simple fact. The I/O-voltage for a particular I/O-Bank is set in the hardware, not in the pin assignments. The pin assignments can a best select a legal I/O standard for a certain I/O bank. The Dev. Kit's reference manual lists the available I/O standards for HSMC connected pins, they are all 2.5V, as far as I see.

    But there is no problem, cause another of your assumptions is also wrong. Most (all?) 3.3V CAN drivers can be driven reliably by 2.5V CMOS logic. For the receiver, the 2.5V FPGA input can be driven by 3.3V logic, if you provide a source sided series termination to avoid overshoots above the permitted input level. A resistive divider to 2,5V or a diode clamp circuit would be an even better solution.