Use of bi-directional input/output circuits to maintain configuration state during concurrent maintenance
Original Publication Date: 2000-Jul-01
Included in the Prior Art Database: 2003-Jun-19
A data processing system is generally designed so that the majority of its components can be replaced without adversely affecting the function of the product during the replacement procedure. To achieve this many components are mounted on a single, removable card which may be replaced while the rest of the product continues to function. If this removable card contains components which assert lines determining the configuration of other parts of the product then this configuration will be lost when the card is removed from the product. Should any other components need to read the configuration while this card is removed then they assume default values which may be undesirable. One of the components of the product which uses these configuration lines is a microcontroller which reads the lines through general purpose input/output circuits. Normally these circuits are set up as inputs to read the configuration lines. When the microcontroller detects that the card containing the configuration asserting components has been removed, the general purpose input/output circuits are quickly changed to outputs and assert the configuration lines to the state previously read. When the card is re-inserted the general purpose input/output circuits are quickly changed back to inputs reading the lines which are now asserted in the normal way. This means that any other components of the product which need to read the configuration lines when the removable card is absent can do so and will read the desired configuration rather than default values.