The mikroPascal PRO for 8051 provides routines for implementing Software SPI communication. These routines are hardware independent and can be used with any MCU. The Software SPI Library provides easy communication with other devices via SPI: A/D converters, D/A converters, MAX7219, LTC1290, etc.

• SPI to Master mode
• Clock value = 20 kHz.
• Clock idle state low.
• Data sampled at the middle of interval.
• Data transmitted at low to high edge.

Note: The Software SPI library implements time-based activities, so interrupts need to be disabled when using it.

External dependencies of Software SPI Library

Library Routines

• Soft_SPI_Init
• Soft_SPI_Read
• Soft_SPI_Write

Soft_SPI_Init

// soft_spi pinout definition
var SoftSpi_SDI : sbit at P0_4_bit;
    SoftSpi_SDO : sbit at P0_5_bit;
    SoftSpi_CLK : sbit at P0_3_bit;
...
Soft_SPI_Init(); // Init Soft_SPI

Soft_SPI_Read

var data_read : word;
    data_send : byte;
...
// Read a byte and assign it to data_read variable
// (data_send byte will be sent via SPI during the Read operation)
data_read := Soft_SPI_Read(data_send);

Soft_SPI_Write

// Write a byte to the Soft SPI bus
Soft_SPI_Write(0xAA);

Library Example

This code demonstrates using library routines for Soft_SPI communication. Also, this example demonstrates working with Microchip's MCP4921 12-bit D/A converter.

program Soft_SPI;

var i, received_data : byte;

// Port Expander module connections
var SPExpanderRST : sbit at P0_6_bit;
var SPExpanderCS  : sbit at P0_7_bit;
// End Port Expander module connections

var SoftSpi_CLK : sbit at P0_2_bit;
var SoftSpi_SDI : sbit at P0_3_bit;
var SoftSpi_SDO : sbit at P0_4_bit;

begin
  i := 0;
  WDTCN   := 0xDE;                  // Sequence for
  WDTCN   := 0xAD;                  //   disabling the watchdog timer
  OSCICN  := 0x83;                  // Enable internal oscillator (24.5MHz divided by 1)
  P0MDOUT := P0MDOUT or %11010101;  // Configure P0.7(CS), P0.6(RST), P0.4(MOSI), P0.2(SCK)
                                    //   and P0.0(TX) pin as push-pull

  UART1_Init(4800);                 // Initialize UART module at 4800 bps
  Delay_ms(100);                    // Wait for UART module to stabilize
  UART1_Write_Text('Start');

  SPI_Rd_Ptr := @Soft_SPI_Read;                 // Link Port Expander Library to Software SPI library

  Expander_Init(0);                             // Initialize Port Expander

  Expander_Set_DirectionPortA(0, 0x00);         // Set Expander's PORTA to be output

  Expander_Set_DirectionPortB(0, 0xFF);         // Set Expander's PORTB to be input
  Expander_Set_PullUpsPortB(0, 0xFF);           // Set pull-ups to all of the Expander's PORTB pins

  while TRUE do                                 // Endless loop
    begin
      Expander_Write_PortA(0, i);               // Write i to expander's PORTA
      Inc(i);
      received_data := Expander_Read_PortB(0);  // Read expander's PORTB
      UART1_Write(received_data);               //   and send it to UART
      Delay_ms(100);
    end;
end.

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