| 摘要 |
A programmable register stores a control bit for settting the logic polarity of an I/O signal at an I/O terminal of an integrated circuit. The I/O polarity control signal is combined in an exclusive-OR logic circuit with the I/O signal to provide a given logic polarity for the I/O signal. For a bi-directional I/O terminal, two exclusive-OR gates are used, one for controlling polarity of output signals from the integrated circuit to the I/O terminal and the other for controlling the polarity of input signals to the integrated circuits which are received at the I/O terminal. The control of the I/O signal polarity is particularly useful for a disk-drive controller which interfaces with different magnetic disk drive units, having different I/O signal polarity requirements.
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