
MC68336/376
CONFIGURABLE TIMER MODULE 4
MOTOROLA
USER’S MANUAL
Rev. 15 Oct 2000
10-11
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 compara-
tor, though internally, channel B has two data registers (B1 and B2). DASM operating
mode determines which register is software accessible. Refer to Table 10-3.
Register contents are always transferred automatically at the correct time so that the
minimum pulse (measured or generated) is just one time base bus count. The A and
B data registers are always read/write registers, accessible via the CTM4 submodule
bus.
The CTM4 has four DASMs. Figure 10-5 shows a block diagram of the DASM.
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
Table 10-3 Channel B Data Register Access
Mode
Data Register
Input Capture
(IPWM, IPM, IC)
Registers A and B2 are used to hold the captured values. In these modes,
the B1 register is used as a temporary latch for channel B.
Output Compare
(OCA, OCAB)
Registers A and B2 are used to define the output pulse. Register B1 is not
used in these modes.
Output Pulse Width
Modulation Mode
(OPWM)
Registers A and B1 are used as primary registers and hidden register B2 is
used as a double buffer for channel B.