MC68F375
CONFIGURABLE TIMER MODULE (CTM9)
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
13-38
13.5.5.3 DASMB — DASM Data Register B
DASMB is the data register associated with channel B; its use varies with the different
modes of operation. Depending on the mode selected, software access is to register
B1 or register B2.
In the DIS mode, DASMB can be accessed to prepare a value for a subsequent mode
selection. In this mode, register B1 is accessed in order to prepare a value for the
OPWM mode. Unused register B2 is hidden and cannot be read, but is written with the
same value when register B1 is written.
In the IPWM mode, DASMB contains the captured value corresponding to the leading
edge of the measured pulse. In this mode, register B2 is accessed; buffer register B1
is hidden and cannot be accessed.
In the IPM and IC modes, DASMB contains the captured value corresponding to the
most recently detected period edge (rising or falling edge). In this mode, register B2 is
accessed; buffer register B1 is hidden and cannot be accessed.
In the OCB and OCAB modes, DASMB is loaded with the value corresponding to the
trailing edge of the pulse to be generated. Writing to DASMB in the OCB and OCAB
modes also enables the corresponding channel B comparator until the next successful
comparison. In this mode, register B2 is accessed; buffer register B1 is hidden and
cannot be accessed.
In the OPWM mode, DASMB is loaded with the value corresponding to the trailing
edge of the PWM pulse to be generated. In this mode, register B1 is accessed; buffer
register B2 is hidden and cannot be accessed.
13.6 Pulse Width Modulation Submodule (PWMSM)
The purpose of the pulse width modulation submodule (PWMSM) is to create a vari-
able pulse width output signal at a wide range of frequencies, independent of other
CTM9 output signals. The PWMSM includes its own counter, and thus does not use
the CTM9 time-base buses. The PWMSM pulse width can vary from 0.0 percent to
100.0 percent, with up to 16 bits of resolution. The finest output resolution is the MCU
system clock time divided by two (for a system clock of 16.78 MHz, the finest output
pulse width resolution is 119 nanoseconds). With the full 16 bits of resolution and the
first stage prescaler divide-by-2 clock selection, the period of the PWM output can
DASM3B — DASM Data Register B
0xYF F21C
DASM4B
0xYF F224
DASM9B
0xYF F24C
DASM10B
0xYF F254
MSB
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
LSB
0
MSB
LSB
RESET:
0
F
re
e
sc
a
le
S
e
m
ic
o
n
d
u
c
to
r,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
c
..
.