mc9s12xd256 Freescale Semiconductor, Inc, mc9s12xd256 Datasheet - Page 377

• Manufacturer Part Number: mc9s12xd256
• Description: Hcs12x Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

8.3.2.12
Each channel has a dedicated 8-bit up/down counter which runs at the rate of the selected clock source.
The counter can be read at any time without affecting the count or the operation of the PWM channel. In
left aligned output mode, the counter counts from 0 to the value in the period register - 1. In center aligned
output mode, the counter counts from 0 up to the value in the period register and then back down to 0.
Any value written to the counter causes the counter to reset to $00, the counter direction to be set to up,
the immediate load of both duty and period registers with values from the buffers, and the output to change
according to the polarity bit. The counter is also cleared at the end of the effective period (see
Section 8.4.2.5, “Left Aligned Outputs”
When the channel is disabled (PWMEx = 0), the PWMCNTx register does not count. When a channel
becomes enabled (PWMEx = 1), the associated PWM counter starts at the count in the PWMCNTx
register. For more detailed information on the operation of the counters, see
Counters”.
In concatenated mode, writes to the 16-bit counter by using a 16-bit access or writes to either the low or
high order byte of the counter will reset the 16-bit counter. Reads of the 16-bit counter must be made by
16-bit access to maintain data coherency.
Read: Anytime
Write: Anytime (any value written causes PWM counter to be reset to $00).
8.3.2.13
There is a dedicated period register for each channel. The value in this register determines the period of
the associated PWM channel.
The period registers for each channel are double buffered so that if they change while the channel is
enabled, the change will NOT take effect until one of the following occurs:
Freescale Semiconductor
Writing to the counter while the channel is enabled can cause an irregular PWM cycle to occur.
Reset
•
•
•
W
R
The effective period ends
The counter is written (counter resets to $00)
The channel is disabled
Bit 7
PWM Channel Counter Registers (PWMCNTx)
PWM Channel Period Registers (PWMPERx)
0
0
7
Writing to these registers when in special modes can alter the PWM
functionality.
Figure 8-14. PWM Channel Counter Registers (PWMCNTx)
0
0
6
6
MC9S12XDP512 Data Sheet, Rev. 2.17
0
0
5
5
and
Section 8.4.2.6, “Center Aligned Outputs”
NOTE
NOTE
0
0
4
4
0
0
3
3
Chapter 8 Pulse-Width Modulator (S12PWM8B8CV1)
0
0
2
2
Section 8.4.2.4, “PWM Timer
0
0
1
1
for more details).
Bit 0
0
0
0
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