STR750 implementation example

AN2682 - Application note

12/15

First, the STR750 peripherals are initialized:

●

The TIM0/PWM timer is configured in PWM mode with a period and duty cycle

corresponding to the user defined CLK frequency.

●

The SSP0 is configured in slave mode, rising edge clock (CPOL=1, CPHA=1), 16 bit

format, 8 words Transmit and Receive FIFO depth.

●

The DMA is configured to enable SSP Transmit (from memory to peripheral) on

channel 0 and SSP Receive (from peripheral to memory) on channel 1.

The STR75x microcontroller performs two main functions:

1.

Configuration function: the microcontroller gets the user-defined Conf_Reg register

value from the DEFINE statements, then sets Start pin low and transmit the three bits

clocked by Conf falling edge.

2.

Communication function: After setting the Start signal high, only the DMA is active

and it loads the Transmit FIFO from memory whenever it is half empty and loads the

memory from the Receive FIFO whenever it is half full. The CPU is totally free for any

other application tasks.

Figure 10.

STR75x firmware flowchart

In this flowchart, the DMA function is not shown because it works in the background and has

no effect on the CPU. The same flowchart can be used for STR91x.

The STR75x firmware can be easily tailored to any STR91x or STM32 microcontroller.

Begin

Initialize peripherals

(SSP, TIM0, DMA, GPIO...)

Generate CLK

Configuration mode

Set Conf_Reg

Communication mode

END

End Of Count

Stop PWM counter

Clear Flags

END

End Of Count