MC68336/376
CONFIGURABLE TIMER MODULE 4
MOTOROLA
USER’S MANUAL
Rev. 15 Oct 2000
10-19
NOTE
A duty cycle of 100% is not possible when the output period is set to
65536 PWM clock periods (which occurs when PWMB2 is set to
$0000). In this case, the maximum duty cycle is 99.998% (100 x
65535/65536).
Even when the duty cycle is 0% or 100%, the PWMSM counter
continues to count.
10.9.11 PWMSM Registers
The PWMSM contains a status/interrupt/control register, a period register, a pulse
width register, and a counter register. All unused bits and reserved address locations
return zero when read. Writes to unused bits and reserved address locations have no
effect. The CTM4 contains four PWMSMs, each with its own set of registers. Refer to
mation concerning PWMSM register and bit descriptions.
10.10 CTM4 Interrupts
The CTM4 is able to generate as many as eleven requests for interrupt service. Each
submodule capable of requesting an interrupt can do so on any of seven levels. Sub-
modules that can request interrupt service have a 3-bit level number and a 1-bit
arbitration number that is user-initialized.
The 3-bit level number selects which of seven interrupt signals on the IMB are driven
by that submodule to generate an interrupt request. Of the four priority bits provided
by the IMB to the CTM4 for interrupt arbitration, one of them comes from the chosen
submodule, and the BIUSM provides the other three. Thus, the CTM4 can respond
with two of the 15 possible arbitration numbers.
During the IMB arbitration process, the BIUSM manages the separate arbitration
among the CTM4 submodules to determine which submodule should respond. The
CTM4 has a fixed hardware prioritization scheme for all submodules. When two or
more submodules have an interrupt request pending at the level being arbitrated on
the IMB, the submodule with the lowest number (also the lowest status/interrupt/con-
trol register address) is given the highest priority to respond.
If the CTM4 wins arbitration, it responds with a vector number generated by concate-
nating VECT[7:6] in BIUMCR and the six low-order bits specified by the number of the
submodule requesting service. Table 10-7 shows the allocation of CTM4 submodule
numbers and interrupt vector numbers.