LP55231 datasheet(40/59 Pages) TI2

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DIMMING

CONTROL

STEP COUNT

STEP TIME

SPAN =

187.5ms

TIME ELAPSED (ms)

375

750

1125

1500

140

141

142

143

144

145

146

147

148

RAMP INSTRUCTION

LP55231

SNOSCR5D – MARCH 2013 – REVISED DECEMBER 2016

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Table 8. Ramp Instructions (continued)

NAME

VALUE (d)

DESCRIPTION

(2)

Valid for variables.

# of

increments(1)

0 - 255

The number of increment/decrement cycles. Note: Value 0 takes the same time as increment by 1, but

it is the wait instruction.

step time(2)

0 - 3

One ramp increment done in (step time) x (prescale).

Step time is loaded with the value (5 LSB bits) of the variable defined below.

0 = local variable A

1 = local variable B

2 = global variable C

3 = register address 3CH variable D value, or register address 42H value.

The value of the variable should be from 00001b to 11111b (1d to 31d) for correct operation.

# of

increments(2)

0 - 3

The number of increment/decrement cycles. Value is taken from variable defined below:

0 = local variable A

1 = local variable B

2 = global variable C

3 = register address 3CH variable D value, or register address 42H value.

(1)

(i) Valid for numerical operands. (ii) Valid for variables.

7.6.4.2 Ramp Instruction Application Example

Suppose that the LED dimming is controlled according to the linear scale and effective PWM value at the

moment t = 0 is 140d (approximately 55%), as shown in the figure below, and we want to reach a PWM value of

148d (approximately 58%) at the moment t = 1.5 s. The parameters for the RAMP instruction are:

•

Prescale = 1

→ 15.625 ms cycle time

•

Step time = 12

→ step time span is 12 × 15.625 ms = 187.5 ms

•

Sign = 0

→ increase PWM output

•

# of increments = 8

→ take 8 steps

Figure 26. Example Of Ramp Instruction

7.6.4.3 Set_PWM

This instruction is used for setting the PWM value on the outputs D1 to D9 without any ramps. Set PWM output

value from 0 to 255 with PWM value bits [7:0]. Instruction execution takes sixteen 32-kHz clock cycles (=488 µs).

NAME

VALUE (d)

DESCRIPTION

PWM value (i)(1)

0 - 255

PWM output duty cycle 0 - 100%

variable (ii)(1)

0 - 3

0 = local variable A

1 = local variable B

2 = global variable C

3 = register address 3CH variable D value, or register address 42H value.

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