On Fri, 4 Apr 2008, Eric H. Johnson wrote:
> Date: Fri, 4 Apr 2008 04:13:28 -0400
> From: Eric H. Johnson <[EMAIL PROTECTED]>
> Reply-To: "Enhanced Machine Controller (EMC)"
> <[email protected]>
> To: "'Enhanced Machine Controller (EMC)'" <[email protected]>
> Subject: [Emc-users] Another Mesa question
>
> John, Peter, et al.
>
> I found the problem with the "current" (Mesa 7I33 AUX Power). It was really
> stupid. It is a 0 to 10V analog for laser power where the sign matters. The
> value was coming out negative. I changed the gain on the DAC to -1, and
> everything is working fine.
>
> The problem I have now is with the outputs coming on while the computer
> boots. On this laser, E-Stop is a last resort and has an E-Stop separate
> from the CNC. Normally one has to use its startup and shutdown method. Thus,
> if the laser is on, it starts going through its startup sequence while the
> computer is booting, because the m5i20 outputs are on. Is there any way to
> force these outputs off prior to when EMC starts?
>
> Thanks,
> Eric
>
The default state of 5I20 outputs is high at power up. This is because all
FPGA pins float before the FPGA is programmed, and all I/O pins have 3.3K
pullup resistors. This startup state is appropriate for our daughter cards
which either have active low signals to turn outputs ON (like the 7I37) or
have active low enables (like the 7I33). This is also whats is normally
desired when connected to I/O module racks (All output devices OFF at power
up).
If you wish a certain pin to power up in a low state, you can add an external
pull down resistor, but this must be a low enough value to overcome the
built-in 3.3K pullups (say 500 Ohm).
If your external circuitry will work with more pins pulled down, you can
reverse the appropriate socketed 10 pin SIP 3.3K pullup resistor network, (by
pulling it out of the socket and rotating it end for end and re-installing)
This will pull down a group of 8 I/O pins, so they power up in a low state.
Peter Wallace
Mesa Electronics
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