Motorola MCF5282, MCF5281 user manual Signal Connection Considerations, Result Word Table

Models: MCF5282 MCF5281

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Signal Connection Considerations

Any conversion in progress for a queue is aborted when that queue’s operating mode is changed to disabled. Putting a queue into the disabled mode does not power down the converter.

Changing a queue’s operating mode to another valid mode aborts any conversion in progress. The queue restarts at its beginning once an appropriate trigger event occurs.

For low-power operation, the stop bit can be set to prepare the module for a loss of clocks. The QADC aborts any conversion in progress when stop mode is entered.

When the QADC debug bit is set and the CPU enters background debug mode, the QADC freezes at the end of the conversion in progress. After leaving debug mode, the QADC resumes queue execution beginning with the next CCW entry. Refer to Section 27.3.1” for more information.

27.8.11 Result Word Table

The result word table is a 64 half-word (128 byte) long by 10-bit wide RAM. An entry is written by the QADC after completing an analog conversion specified by the corresponding CCW table entry. The result word table can be read or written, but in normal operation is only read to obtain analog conversions from the QADC. Unimplemented bits read as 0s and writes have no effect.

NOTE

Although the result RAM can be written, some write operations, like bit manipulation, may not operate as expected because the hardware cannot access a true 16-bit value.

While there is only one result word table, the half-word (16-bit) data can be accessed in three different data formats:

Right justified with 0s in the higher order unused bits

Left justified with the most significant bit inverted to form a sign bit, and 0s in the unused lower order bits

Left justified with 0s in the lower order unused bits

The left justified, signed format corresponds to a half-scale, offset binary, two’s complement data format. The address used to read the result table determines the data alignment format. All write operations to the result word table are right justified.

27.9 Signal Connection Considerations

The QADC requires accurate, noise-free input signals for proper operation. This section discusses the design of external circuitry to maximize QADC performance.

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MCF5282 User’s Manual

MOTOROLA

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Motorola MCF5282, MCF5281 user manual Signal Connection Considerations, Result Word Table