Cypress S6J3200 Series, Manual

Page: 984 / 1355

CHAPTER 26:PCMPWM
S6J3200 Series Hardware Manual Document Number: 002-04852 Rev. *G 983
3.
Operation of the PCMPWM
This section describes the operation of the PCMPWM module.
3.1.
Description of the PCM to PWM Conversion Process
The actual conversion of the PCM data samples to a PWM signal is done in the PCM to PWM converter
as shown in Figure 2-1. The first step is a conversion of the signed PCM sample to an unsigned PCM
compare value. How this is done depends on the operation mode. In low-pass filter mode and simplified
H-bridge mode the step is a simple addition. The value to be added is configured in the
PCMPWMi_PCMOFFS register. In full H-bridge mode the PCM compare value is the absolute value of
the PCM data sample. Table 3-1 summarizes how the PCM compare value is computed in each operation
mode.
Table 3-1 Inactive Output Values
Operation Mode Computation
Low Pass Filter PCM PCMOFFS
Simplified H-Bridge PCM PCMOFFS
Full H-Bridge |PCM sample|
The second step of the PCM to PWM conversion process comprises a free running counter and two
comparators. The counter counts up from zero to a programmable maximum value. The maximum value
is given by the PCMPWMi_COUNTP register. Whenever the counter has reached its maximum value, it
wraps around to zero. The counter value is continuously compared against two values. The first value is
zero and the second is the PCM compare value. The outputs of the two comparators are fed into the
actual PWM signal generation. Depending on the operation mode this final block generates the actual
PWM signals. Table 3-2 summarizes the logic for generating the PWM signals from the two comparator
outputs. Please note the signal levels in the table are for the output polarity with
PCMPWMi_OCTRL:LEVLx set to logic 1.
Table 3-2 Generation of PWM Output Signals
Event
Low-Pass
Filter Mode
Simplified
H-Bridge Mode
Full H-Bridge Mode
AH AH AL AH AL BH BL
Counter = 0
PCM sample positive
↑ ↑ ↓
↑ ↓ 0 1
PCM sample = 0 0 1 0 1
PCM sample negative 0 1 ↑ ↓
Counter = PCM
compare value
PCM sample positive
↓ ↓ ↑
↓ ↑ 0 1
PCM sample = 0 0 1 0 1
PCM sample negative 0 1 ↓ ↑
Note:
−
In case the PCM compare value is zero, the event given for equality with the PCM compare value
takes precedence.