DISABLE DEVICE Section

The DISABLE DEVICE section describes how to set the device into a 'safe' state, so that the connection test can avoid driving any nets while they are also driven from the device itself.

There are two ways of describing pins in this section:

Preventing the device driving nets

If you can control the chip select pin from a JTAG device, for instance, you can pull it high to stop the device driving any nets. E.g.:

DEVICE NAME := "test"
    DISABLE DEVICE
        nCS0 := 1;
        CS1 := 0;
        nOE := 1;
    END;
END;

If you cannot prevent the device driving JTAG nets

If the device always drives certain nets, the connection test must not drive those nets. The value 'Z' is used to indicate this. E.g.:

DEVICE NAME := "test"
    DISABLE DEVICE
        DATA_OUT := Z;
        nIRQ := Z;
    END;
END;

Pins can be set to one of three values in this section: 1, 0 or Z.

Pins which are not controllable from any JTAG devices may also be added to this section for completeness - and to allow the device file to be reusable between boards - but XJTAG will emit warnings that it can't drive those pins.

Pins listed in the DISABLE DEVICE section behave identically to those listed in the CONSTANT PINS section in the project file. It is generally better to use the DISABLE DEVICE section, however, since the device file can be re-used more easily if all the necessary information is present.