Freescale-semiconductor ColdFire MCF52210 Manual de usuario descargar pdf (Pagina 483)

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Pulse-Width Modulation (PWM) Module

MCF52211 ColdFire® Integrated Microcontroller Reference Manual, Rev. 2

Freescale Semiconductor 27-9

27.2.8 PWM Scale B Register (PWMSCLB)

PWMSCLB is the programmable scale value used in scaling clock B to generate clock SB. Clock SB is

generated according to the following equation:

Eqn. 27-2

Any value written to this register causes the scale counter to load the new scale value (PWMSCLB).

27.2.9 PWM Channel Counter Registers (PWMCNTn)

Each channel has a dedicated 8-bit up/down counter that runs at the rate of the selected clock source,

PWMCLK[PCLKn]. The user can read the counters 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 minus 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. Therefore, given the same value in the period register,

center-aligned mode is twice the period of left-aligned mode.

Any value written to the counter causes the counter to reset to 0x00, the counter direction to be set to up

for center-aligned mode, the immediate load of 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 27.3.2.5, “Left-Aligned Outputs”

and Section 27.3.2.6, “Center-Aligned Outputs” for more details). When the channel is disabled

IPSBAR

Offset:

0x1B_0009 (PWMSCLB) Access: User Read/Write

76543210

SCALEB

Reset:00000000

Figure 27-9. PWM Scale B Register (PWMSCLB)

Table 27-9. PWMSCLB Field Descriptions

Field Description

7–0

SCALEB

Divisor used to form Clock SB from Clock B.

Clock SB

Clock B

2PWMSCLB×

----------------------------------------

SCALEB Value

0x00 256

0x01 1

0x02 2

... ...

0xFF 255

1 2 ... 478 479 480 481 482 483 484 485 486 487 488 ... 575 576

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Freescale-semiconductor ColdFire MCF52210 Manual de usuario Pagina 483

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