
MC68F375
CONFIGURABLE TIMER MODULE (CTM9)
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
13-19
is serviced, the FLAG bit should be cleared by the servicing routine before returning
from that routine. If a subsequent output compare occurs while the FLAG bit is set, the
internal output compare functions normally, and the FLAG bit remains set.
In OP mode, the IN bit value reflects the logic state on the output of the output flip-flop.
13.4.2 SASM Interrupts
Each channel in the dual-channel SASM has separately enabled and initiated inter-
rupts and they each have their own unique vector number and address. However, they
are both assigned to the same interrupt level and arbitration priority by the IL[2:0] and
IARB3 bits in the SICA register.
A valid SASM interrupt is recognized when the FLAG bit is set, the corresponding IEN
bit is set and the interrupt level defined by bits IL[2:0] is not equal to zero.
The FLAG bit is a status bit that indicates, when set, that an input capture or output
compare has occurred on the corresponding single action channel.
The relative priority of these sources of interrupt is fixed and channel A has a higher
priority than channel B.
13.4.3 Freeze Action on the SASM
When the IMB FREEZE signal is recognized, the SASM input capture and output com-
pare functions are halted. As soon as the FREEZE signal is negated, SASM actions
resume as if nothing had happened. During freeze, the IN bits of the SIC registers
(SICA and SICB) are readable and return the levels present at the input pins if an input
mode is in operation, or the output value if an output mode is in operation (see 13.4.4.1 the force output function remains available, allowing the software to output the desired
level (a useful feature for debugging). All SASM registers are accessible during freeze.
13.4.4 SASM Registers
The SASM register map comprises eight 16-bit register locations. As shown in Table 13-6, the register block contains two SASM registers for each channel and four
reserved registers. All unused bits and reserved address locations return zero when
read by the software. Writing to unused bits and reserved address locations has no
meaning nor effect. All register addresses in this section are specified as offsets from
the base address of the SASM. In CTM implementations featuring multiple SASMs,
each SASM has its own set of registers.
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