MC68336/376
QUEUED ANALOG-TO-DIGITAL CONVERTER MODULE
MOTOROLA
USER’S MANUAL
Rev. 15 Oct 2000
8-31
where queue 2 begins after suspension. By choosing to re-execute all of the sus-
pended queue 2 and subqueue CCWs, all of the samples are guaranteed to have
been taken during the same scan pass. However, a high trigger event rate for
queue 1 can prohibit the completion of queue 2. If this occurs, execution of queue
2 may begin with the aborted CCW entry.
When a queue is disabled, any conversion taking place for that queue is aborted.
Putting a queue into disabled mode does not power down the converter.
When the operating mode of a queue is changed to another valid mode, any
conversion taking place for that queue is aborted. The queue operating restarts
at the beginning of the queue, once an appropriate trigger event occurs.
When placed in low-power stop mode, the QADC aborts any conversion in
progress.
When the FRZ bit in the QADCMCR is set and the IMB FREEZE line is asserted,
the QADC freezes at the end of the current conversion. When FREEZE is negat-
ed, the QADC resumes queue execution beginning with the next CCW entry.
8.12.8 Result Word Table
The result word table is a 40-word long, 10-bit wide RAM. The QADC writes a result
word after completing an analog conversion specified by the corresponding CCW. The
result word table can be read or written, but in normal operation, software reads the
result word table to obtain analog conversions from the QADC. Unimplemented bits
Table for register descriptions.
While there is only one result word table, the data can be accessed in three different
alignment formats:
1. Right justified, with zeros in the higher order unused bits.
2. Left justified, with the most significant bit inverted to form a sign bit, and zeros
in the unused lower order bits.
3. Left justified, with zeros in the unused lower order bits.
The left justified, signed format corresponds to a half-scale, offset binary, two’s com-
plement data format. The data is routed onto the IMB according to the selected format.
The address used to access the table determines the data alignment format. All write
operations to the result word table are right justified.
8.13 Interrupts
The QADC supports both polled and interrupt driven operation. Status bits in QASR
reflect the operating condition of each queue and can optionally generate interrupts
when enabled by the appropriate bits in QACR1 and/or QACR2.
8.13.1 Interrupt Sources
The QADC has four interrupt service sources, each of which is separately enabled.
Each time the result is written for the last CCW in a queue, the completion flag for the
corresponding queue is set, and when enabled, an interrupt request is generated. In