| 摘要 |
Two cascaded eight-bit maskable counters (62) and (64) provide a sixteen-bit output, for instance, to a digital-to-analog converter (10). Each of the counters (62) and (64) is a maskable counter that is operable to mask off a programmable number of the least significant bits therein. The next adjacent bit thereto comprises a virtual least significant bit. During the counting operation, the count is initiated at the virtual least significant bit such that the virtual least significant bit is clocked for each counting cycle. An initial value is first loaded into the counter (62) and (64) on a data bus (74). Thereafter, masked data is loaded into the counters (62) and (64) on the same data bus (74) to define the ones of the least significant bits that are masked off. In such a manner, the overall resolution of the counter can be varied without varying the clock rate to the counter. By masking off the bits, the count is automatically incremented by a value equal to that represented by the masked off bits for each cycle of the clock input to the counter.
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