How to Program Parallel Slave Port (PSP) in PIC16F877A

The following code demonstrate how to use parallel slave port module. The controller offers a mechanism by which an 8-bit parallel bidirectional data transfer can be achieved between a PIC16F877A and other PSP supporting devices. The PIC16F877A's Port-D and Port-E are used in this data transfer. For this data transfer, Port-D is configured as a parallel slave port (PSP) by setting bit-4 of TRISE Register. The pins of Port-E function as control pins for data transfer. The code is written in “mikroC PRO for PIC v.6.6.3” IDE and simulation is done with Proteus 8.0 SP0. At the end of code, you can find complete project files for download.

UUT Code in mikroC

// function proto-type

void PSP_Setting(void);

void main(void)

{

// portb as input port

TRISB = 0xFF;

// portc as output port

TRISC = 0x00;

// portc init to 0x00

PORTC = 0x00;

PSP_Setting();

while(1)

{

// write request to PSP

if(TRISE.IBF == 1)

{

PORTC = PORTD;

// auto clear TRISE.IBF

}

// read request from PSP

// TRISE.IBF == 0

else

{

PORTD = PORTB;

}

}

}

void PSP_Setting(void)

{

// select porte as digital i/o

ADCON1.PCFG3 = 0;

ADCON1.PCFG2 = 0;

ADCON1.PCFG1 = 1;

ADCON1.PCFG0 = 0;

// enable PSP mode

TRISE.PSPMODE = 1;

// clear input buffer overflow error

TRISE.IBOV = 0;

// clear output buffer full bit

TRISE.OBF = 0;

// clear input buffer full bit

TRISE.IBF = 0;

}

PSP Tester Code in mikroC

sbit nRD_Dir at TRISB.B0;

sbit nWR_Dir at TRISB.B1;

sbit nCS_Dir at TRISB.B2;

sbit WR_RD_SEL_Dir at TRISB.B7;

sbit nRD at PORTB.B0;

sbit nWR at PORTB.B1;

sbit nCS at PORTB.B2;

sbit WR_RD_SEL at PORTB.B7;

//void PSP_Setting(void);

void WriteActive(void);

void ReadActive(void);

void IdleBus(void);

void main(void)

{

unsigned char count = 0x00;

unsigned char read_buf = 0x00;

// direction as output

nRD_Dir = 0;

nWR_Dir = 0;

nCS_Dir = 0;

// direction as input

WR_RD_SEL_Dir = 1;

// init to 1 because all signals are

// active low

nRD = 1;

nWR = 1;

nCS = 1;

// portc as output port

TRISC = 0x00;

// portc init to 0x00

PORTC = 0x00;

// make as output

TRISD = 0x00;

Delay_ms(1);

// pulse to init PSP

WriteActive();

while(1)

{

if(WR_RD_SEL == 1)

{

// make as output

TRISD = 0x00;

Delay_ms(1);

// data write to PSP

WriteActive();

PORTD = count++;

Delay_ms(5);

// idle bus

IdleBus();

Delay_ms(10);

}

if(WR_RD_SEL == 0)

{

// make as input

TRISD = 0xFF;

Delay_ms(1);

// data read from PSP

ReadActive();

read_buf = PORTD;

PORTC = read_buf;

Delay_ms(5);

// idle bus

IdleBus();

Delay_ms(10);

}

}

}

void PSP_Setting(void)

{

// select porte as digital i/o

ADCON1.PCFG3 = 0;

ADCON1.PCFG2 = 0;

ADCON1.PCFG1 = 1;

ADCON1.PCFG0 = 0;

// enable PSP mode

TRISE.PSPMODE = 1;

// clear input buffer overflow error

TRISE.IBOV = 0;

// clear output buffer full bit

TRISE.OBF = 0;

// clear input buffer full bit

TRISE.IBF = 0;

}

void WriteActive(void)

{

nRD = 1;

nWR = 0;

nCS = 0;

Delay_us(100);

}

void ReadActive(void)

{

nRD = 0;

nWR = 1;

nCS = 0;

Delay_us(100);

}

void IdleBus(void)

{

nRD = 1;

nWR = 1;

nCS = 1;

Delay_us(100);

}

Download Files

For download “mikroC PRO for PIC” project and “Proteus 8.0” simulation files, click here.