AS3661 datasheet(69/87 Pages) AMSCO

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AS3661

Datasheet - D e t a i l e d D e s c r i p t i o n

Figure 29. RAMP Instruction Example

8.12.2 RAMP (Variables)

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 will have no effect on instruction

execution. Again, at each ramp step the output is incremented/decremented by one unless step time is 0 or 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

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 0x06, 0x07, or 0x08 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.

COMPILER COMMAND SYNTAX: RWV, prescale[1], sign[1], step time[2], number of increments[2];

Table 76. RWV Parameter Description

Name

Value

Description

prescale

Divides master clock (32 768 Hz) by 16 = 2048 Hz -> 0.488 ms cycle time

Divides master clock (32 768 Hz) by 512 = 64 Hz -> 15.625 ms cycle time

sign

Increase PWM output

Decrease PWM output

step time

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.

local variable A

local variable B

local variable C

value.

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

correct operation.

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