HC08 Timer Beans Implementation Details

The peripheral names and numbers used within this chapter are related to MC68HC908AZ60 CPU. Other derivatives of HC08 family contain analogous timers (with different name or structure). The 68HC908AZ60 contains two timer modules TIMA and TIMB. Each one of these modules is based on a 16-bit counter that can operate as a free-running counter or a modulo up-counter. TIMA module has six channels and TIMB has two channels that can be programmed independently as input capture or output capture channels. Please see more details on timer modules in the CPU manual. For details on another HC08/HCS08 family members please use CPU Parameters Overview window or see a documentation of the appropriate CPU.

 

Figure 1 - Timer A block diagram based on manufacturer documentation

Timer peripheral selection, allocation and timing settings are available in the Bean Inspector of the selected bean and overview of peripheral allocation is also available in Target CPU or Peripheral Usage windows. Please see chapters Bean Inspector, Target CPU and Peripherals Usage for details.

PWM

The PWM bean requires counter register, modulo register and one or two compare registers according to the selected mode. It is possible to use TIMA and TIMB devices. For the TIMA device up to 3 beans can use the device in buffered mode, up to 6 beans can use it in unbuffered mode and for the TIMB 1 bean can use the device in buffered mode and up to 2 in unbuffered mode.

Example 1: Allocation of two PWM beans on the timer TIMA.
PWM#1 uses channel 2 and PWM#2 uses channels 4 and 5 in buffered mode. The registers counter and modulo are shared by both beans (in this case the same period of the generated signal is used for both the counters).

Table 1 - TIMA Regiters Allocation For Example 1

Sharing peripheral with other beans

PWM bean can also share a timer peripheral with another timer beans: TimerInt, RTIshared, TimeDate, FreeCntr8, FreeCntr16, FreeCntr32. The limitation of the PWM when sharing the timer device with these beans is that the period of the PWM must be equal to the full range of the counter (The timing dialog for 'Period' property offers only values corresponding to this condition). Shared beans cannot use the same channels of a timer.

PPG

The PPG bean requires counter register, modulo register and one or two compare registers according the selected mode. There it is possible to use TIMA and TIMB devices. It is not possible to share the un-allocated channels with other beans which means that the PPG bean allocated the whole peripheral.

Example: Allocation of registers of the PPG bean in buffered mode on the timer TIMA.
Channels: 0,1,2 and 3 are free.

TimerOut

The TimerOut bean requires counter register, modulo register and one or two compare registers according the selected mode. It is possible to use TIMA and TIMB devices. For the TIMA device 3-6 TimerOut beans can be used and for the TIMB device 1-2 TimerOut beans can be used.

Example:Allocation of registers with one TimerOut bean in buffered mode on the timer TIMA.
Channels free: 1,2,3,4 and 5 are free. It is possible to allocate the remaining registers. For example with the TimerOut, TimerInt , FreeCntr etc. If more than one bean is used, the other ones work in shared mode. The beans use common counters and modulo registers, and they have a generated signal of the same period.

TimerInt, RTIshared, TimeDate, FreeCntr8, FreeCntr16, FreeCntr32

These beans require counter register, modulo register and eventually compare register according the selected mode. There it is possible to use TIMmod (PITmod), TIMA, TIMB and RTI devices. The TIMA device can use 3-6 TimerOut beans and the TIMB device can use 1-2 TimerOut beans.

Example:Allocation of registers with one Timer Int bean on the timer TIMA.
Channels free: 1,2,3,4 and 5 are free. It is possible to allocate the remaining registers, for example, with the beans of same type and also with TimerOut beans. If more than one bean is used, the other ones work in shared mode. The beans use a common counter and modulo register and a have generated signal of the same period.

Sharing the timer device

Multiple TimerInt, RTIshared, TimeDate, FreeCntr8, FreeCntr16 and FreeCntr32 beans can share the selected timer device. The limitation is that the prescaler value needed to achieve a desired timing must be equal for individual beans.

Example:Allocation of registers with more beans on the timer TIMA.

EventCntr8, EventCntr16, EventCntr32

These beans require counter register and modulo register. It is possible to use the beans for TIMA and TIMB devices. These beans allocate whole peripheral, it is not possible to share unallocated channels with other beans.

Example:Allocation of registers with EventCntr16 bean on the timer TIMA.

Capture

These beans require counter register, modulo register and compare register as input capture latch. It is possible to use the beans for TIMA and TIMB devices.

Example:Allocation of registers with Capture bean on the timer TIMA.
Channels: 0,2,3,4 and 5 are free.

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