LM8322 datasheet(20/42 Pages) NSC

20 / 42 page

14.4 RAMP COMMAND

The RAMP command generates a duty-cycle ramp starting

from the current value. At each step, the ramp counter is in-

cremented or decremented by one, unless it has reached its

its saturation value (0xFF for increment, or 0x00 for decre-

ment). The time for one step is controlled by the PRESCALE

bit and STEPTIME field. The minimum time for one step is

0.49 milliseconds. and the maximum time is about 1 second,

which supports both very fast and very slow ramps. The IN-

CREMENT field specifies the number of steps to be executed

by the command. The maximum value is 126, which corre-

sponds to half of full scale.

There are two special cases in the instruction encoding. If all

bits and fields are 0, it is interpreted as the GO TO START

command. If the STEPTIME field is 0 but any other bit or field

is non-zero, it is interpreted as the SET_PWM command.

PRESCALE

STEPTIME

SIGN

INCREMENT

Bit or Field

Value

Description

PRESCALE

Divide the 32.768 kHz clock by 16

Divide the 32.768 kHz clock by 512

STEPTIME

1–63

Number of prescaled clock cycles per step

SIGN

Increment ramp counter

Decrement ramp counter

INCREMENT

1–126

Number of steps executed by this instruction

14.5 SET_PWM COMMAND

The SET_PWM command loads the ramp counter from the

8-bit DUTYCYCLE field in the instruction.

Please note: Only 0x00 and 0xFF are valid values for the duty

cycle in SET_PWM command. Other values can be estab-

lished by initializing the duty cycle to either 100% or 0%

followed by a RAMP command.

DUTYCYCLE

Bit or Field

Value

Description

DUTYCYCLE

Duty cycle is 0%.

255

Duty cycle is 100%.

14.6 GO_TO_START COMMAND

The GO_TO_START command jumps to the first command

in the script command file.

14.7 BRANCH COMMAND

The BRANCH command jumps to the specified command in

the script command file, with the option of looping for a spec-

ified number of repetitions. Nested loops are not allowed.

LOOPCOUNT

ADDRESS

Field

Value

Description

LOOPCOUNT

Loop until a STOP PWM SCRIPT command is issued by the host.

1–63

Number of repetitions to perform, biased by -1. The range is 0–62 repetitions.

ADDRESS

0–59

Branch destination address in the script command file. If this field is greater than 59, no

looping will be performed.

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