The link below will show you what software upgrade is available for your unit from Humminbird; looks like it should be 6.640 after your unit is upgraded you may be able to use your chip.
http://www.humminbird.com/Category/S...twareVersions/
If not you can find older chip versions here. They have version 2.0, 3.0, 4.0 etc.
Humminbird Fishfinders - Humminbird Depth Sounders - Humminbird ChartPlotters