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MOTOROLA
CONFIGURABLE TIMER MODULE 4
MC68336/376
10-10
USER’S MANUAL
10.7.7 MCSM Registers
The MCSM contains a status/interrupt/control register, a counter, and a modulus latch.
All unused bits and reserved address locations return zero when read. Writes to un-
used bits and reserved address locations have no effect. The CTM4 contains three
MCSMs, each with its own set of registers. Refer to D.7.8 MCSM Status/Interrupt/
Control Registers, D.7.9 MCSM Counter Registers, and D.7.10 MCSM Modulus
Latch Registers for information concerning MCSM register and bit descriptions.
10.8 Double-Action Submodule (DASM)
The double-action submodule (DASM) allows two 16-bit input capture or two 16-bit
output compare functions to occur automatically without software intervention. The
input edge detector can be programmed to trigger the capture function on user-
specified edges. The output flip flop can be set by one of the output compare functions,
and reset by the other one. Interrupt requests can optionally be generated by the input
capture and the output compare functions. The user can select one of two incoming
time bases for the input capture and output compare functions.
Six operating modes allow the DASM input capture and output compare functions to
perform pulse width measurement, period measurement, single pulse generation, and
continuous pulse width modulation, as well as standard input capture and output com-
pare. The DASM can also function as a single I/O pin.
DASM operating mode is determined by the mode select field (MODE[3:0]) in the
DASM status/interrupt/control register (DASMSIC). Table 10-2 shows the different
DASM operating modes.
The DASM is composed of two timing channels (A and B), an output flip-flop, an input
edge detector, some control logic and an interrupt interface. All control and status bits
are contained in DASMSIC.
Channel A consists of one 16-bit data register and one 16-bit comparator. To the user,
channel B also appears to consist of one 16-bit data register and one 16-bit compar-
Table 10-2 DASM Modes of Operation
MODE[3:0]
Mode
Description of Mode
0000
DIS
Disabled — Input pin is high impedance; IN gives state of input pin
0001
IPWM
Input pulse width measurement — Capture on leading edge and the trailing edge
of an input pulse
0010
IPM
Input period measurement — Capture two consecutive rising/falling edges
0011
IC
Input capture — Capture when the designated edge is detected
0100
OCB
Output compare, flag set on B compare — Generate leading and trailing edges of
an output pulse and set the flag
0101
OCAB
Output compare, flag set on A and B compare — Generate leading and trailing
edges of an output pulse and set the flag
0110
—
Reserved
0111
—
Reserved
1xxx
OPWM
Output pulse width modulation — Generate continuous PWM output with 7, 9, 11,
12, 13, 14, 15, or 16 bits of resolution
336376UMBook Page 10 Friday, November 15, 1996 2:09 PM