LP55231 datasheet(39/59 Pages) TI2

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LP55231

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SNOSCR5D – MARCH 2013 – REVISED DECEMBER 2016

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(1)

This opcode is used with numerical operands.

(2)

This opcode is used with variables.

Table 7. LP55231 Data Transfer and Arithmetic Instructions

Inst.

Bit

[15]

Bit

[14]

Bit

[13]

Bit

[12]

Bit

[11]

Bit

[10]

Bit

[9]

Bit [8]

Bit

[7]

Bit [6]

Bit [5]

Bit

[4]

Bit [3] Bit [2]

Bit [1] Bit [0]

target

variable

8-bit value

add(1)

target

variable

8-bit value

add(2)

target

variable

sub(1)

target

variable

8-bit value

sub(2)

target

variable

(1)

Valid for numerical operands.

7.6.4 LED Driver Instructions

7.6.4.1 Ramp

This is the instruction useful for smoothly changing from one PWM value into another PWM value on the D1 to

D9 outputs; in other words, generating ramps (with a negative or positive slope). The LP55231 allows

programming very fast and very slow ramps.

Ramp instruction generates a PWM ramp, using the effective PWM value as a starting value. At each ramp step

the output is incremented/decremented by one unit, unless the number of increments is 0. Time span for one

ramp step is defined with prescale bit [14] and step time bits [13:9]. Prescale = 0 sets 0.49 ms cycle time and

prescale = 1 sets 15.6 ms cycle time; so the minimum time span for one step is 0.49 ms (prescale × step time

span = 0.49 ms × 1) and the maximum time span is 15.6 ms × 31 = 484 ms/step.

Number of increments value defines how many steps are taken during one ramp instruction; increment maximum

value is 255d, which corresponds increment from zero value to the maximum value. If PWM reaches

minimum/maximum value (0/255) during the ramp instruction, ramp instruction is executed to the end regardless

of saturation. This enables ramp instruction to be used as a combined ramp and wait instruction. Note: Ramp

instruction is wait instruction when the increment bits [7:0] are set to zero.

Programming ramps with variables is very similar to programming ramps with numerical operands. The only

difference is that step time and number of increments are captured from variable registers, when the instruction

execution is started. If the variables are updated after starting the instruction execution, it has no effect on

instruction execution. Again, at each ramp step the output is incremented/decremented by one unless increment

is 0. Time span for one step is defined with prescale and step time bits. Step time is defined with variable A, B, C

or D. Variables A, B and C are set with ld-instruction. Variable D is a global variable and can be set by writing the

VARIABLE register (address 3C). LED TEST ADC register (address 42) can be used as a source for the variable

D, as well. Note: Variable A is the only local variable which can be read throughout the serial bus. Of course, the

variable stored in 3CH can be read (and written), too.

Setting register 06H, 07H, or 08H bit LOG_EN high/low sets logarithmic (1) or linear ramp (0). By using the

logarithmic ramp setting the visual effect appears like a linear ramp, because the human eye behaves in a

logarithmic way.

Table 8. Ramp Instructions

NAME

VALUE (d)

DESCRIPTION

prescale

Divides master clock (32.7 kHz) by 16 = 2048 Hz -> 0.488 ms cycle time

Divides master clock (32.7 kHz) by 512 = 64 Hz -> 15.625 ms cycle time

sign

Increase PWM output

Decrease PWM output

step time(1)

1 - 31

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

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