Mode pins

[WayneHowell]

Hi,

I'm using the NE64 part.

Does any one have any advise on using the Port E pins that are used for ModA/B/C during boot.

The problem is that I cannot define the state of these pins during boot as they are connected to bcd switches.

I could add some circuitry to swap between by circuit and open pins during boot, but that is quite a lot of work.

I'm wondering if anyone has come up with a cute solution?

Also is there any may that I can disable checking the Mode pins during boot (I'd be happy for mode to be configured when I program the part)?

Final question: I cannot find in the data sheet whether the Mode pins define open circuit as a logic 1. I'm not clear on whether I select mode by tying the pin hi/lo or open/lo.

Any help much appreciated.

Regards

Wayne

[Lundin]

5V = selected (logical 1), as described in the "MEBI" (Multiplexed External Bus Interface) part of the manual. The file should be called S12MEBIV3.pdf or similar. The mode pins can't be left unconnected. There is no way to disable to mode check, as far as I know.

I assume that you aren't using the external bus or something like that. In that case you would only need MODA=lo, MODB=lo and MODC=hi in order to place the MCU in normal single chip out of reset. Note that MODC has an internal pull-up built-in, unlike MODA and MODB. If however all pins are grounded at startup, the MCU will end up in special single-chip mode, and then there is a smooth solution you can use: have the program write to the MODE register to change from special single chip to normal.