
MC68336/376
QUEUED ANALOG-TO-DIGITAL CONVERTER MODULE
MOTOROLA
USER’S MANUAL
Rev. 15 Oct 2000
8-27
Example 2 in Figure 8-9 is the same as Example 1, except that the PSA bit is set. The
QCLK high phase has 4.5 system clock cycles; the QCLK low phase has 3.5 system
clock cycles.
8.12.5 Periodic/Interval Timer
The QADC periodic/interval timer can be used to generate trigger events at program-
mable intervals to initiate scans of queue 2. The periodic/interval timer is held in reset
under the following conditions:
Queue 2 is programmed to any queue operating mode which does not use the
periodic/interval timer
Interval timer single-scan mode is selected, but the single-scan enable bit is
cleared to zero
IMB system reset or the master reset is asserted
The QADC is placed in low-power stop mode with the STOP bit
The IMB FREEZE line is asserted and the QADC FRZ bit is set to one
Two other conditions which cause a pulsed reset of the timer are:
Rollover of the timer counter
A queue operating mode change from one periodic/interval timer mode to another
periodic/interval timer mode
During the low-power stop mode, the periodic/interval timer is held in reset. Since low-
power stop mode initializes QACR2 to zero, a valid periodic or interval timer mode
must be written to QACR2 when exiting low-power stop mode to release the timer from
reset.
If the QADC FRZ bit is set to one and the IMB FREEZE line is asserted while a periodic
or interval timer mode is selected, the timer is reset after the current conversion
completes. When a periodic or interval timer mode has been enabled (the timer is
counting), but a trigger event has not been issued, freeze mode takes effect immedi-
ately, and the timer is held in reset. When the IMB FREEZE line is negated, the timer
starts counting from zero.
8.12.6 Control and Status Registers
The following paragraphs describe the control and status registers. The QADC has
three control registers and one status register. All of the implemented control register
fields can be read or written. Reserved locations read zero and writes have no effect.
The control registers are typically written once when software initializes the QADC and
bit descriptions.
8.12.6.1 Control Register 0 (QACR0)
Control register QACR0 establishes the QCLK with prescaler parameter fields and
defines whether external multiplexing is enabled.