PC87591L datasheet(148/437 Pages) NSC

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Embedded Controller Modules (Continued)

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Revision 1.07

4.8.3

Cycle Time and Duty Cycle Calculation

The PWM module supports duty cycles in the range of 0% to 100%.

The PWMi output signal cycle time is:

(PRSC + 1) x (CTR + 1) x TCLK

where:

●

TCLK is the core domain clock cycle time (i.e., the PWM input clock).

●

The cycle time may range from 2 x TCLK to 65536 x TCLK.

The PWMi output signal duty cycle (in %, when INVPi is 0) is:

(DCRi + 1) / (CTR + 1) x 100.

Special cases:

●

If the DCRi value is greater than the CTR value, PWMi signal is always low.

●

If DCRi value is equal to the CTR value, PWMi signal is always high.

When Inverse PWMi bit is 1, the value of PWMi output is inverted. i.e., in the period described as 1 is 0 and vice versa.

4.8.4

Power Modes

The PWM is in Low Power mode when Power Mode bit (PWR) in PWM Control Register (PWMCNT) is 0. In this mode, the

PWM input clock is disabled (stopped), but the registers are accessible and maintained. The PWMi signal is 0 when INVPi

bit is 0; it is 1 when INVPi bit is 1.

The PWM is in normal power mode when PWR bit in PWMCNT register is 1. In this mode, the PWM module is enabled, its

registers are accessible and its clock is functional.

The PRSC and CTR registers should be updated during Low Power mode. Otherwise, there may be unpredictable transient

behavior.

4.8.5

PWM Registers

For a summary of the abbreviations used for Register Type, see “Register Abbreviations and Access” on page 34.

PWM Register Map

Clock Pre-Scaler Register (PRSC)

The PRSC register controls the cycle time and the minimal pulse width. PRSC is cleared (0016) on reset.

Location: 00 FD0016

Type: R/W

Mnemonic

Type

PRSC

Clock Pre-Scaler

R/W

CTR

Cycle Time

R/W

DCRi

Duty Cycle 0 to 7

R/W

PWMPOL

PWM Polarity

R/W

PWMCNT

PWM Control

R/W

Bit

76543210

Name

PRSC7-0

Reset

00000000

Bit

Description

7-0

Pre-Scaler Divider Value. The divider of the PWM input clock is the number deﬁned by PRSC7-0 + 1, e.g., a

value of 0016 results in a divide by 1, a value of FF16 results in a divide by 256.

The contents of this register may be changed only when the PWM module is in Low Power mode. Otherwise,

there may be unpredictable results.

PC87591L 데이터시트(PDF) 148 Page - National Semiconductor (TI)

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