MCP23S17 - Three different approaches - ShiftIn/ShiftOut / MSSP+PBP / MSSP+ASM

**gadelhas** · - 1st February 2012, 19:50

Code:

'****************************************************************
'*  Name    : MCP23S17 + MSPP + PBP                             *
'*  Author  : [GADELHAS]                                        *
'*  Notice  : Copyright (c) 2012                                *
'*          : All Rights Reserved                               *
'*  Date    : 31-01-2012                                        *
'*  Version : 1.0                                               *
'*  Notes   :                                                   *
'*          : EASYPICV6 + PIC16F887 + MCP23S17                  *
'****************************************************************
'                              CONFIGS
' ================================================================
@ __CONFIG _CONFIG1, _HS_OSC & _WDT_OFF & _PWRTE_OFF & _MCLRE_ON & _CP_OFF & _BOR_OFF & _DEBUG_OFF & _LVP_OFF & _FCMEN_ON & _IESO_OFF  
@ __CONFIG _CONFIG2, _WRT_OFF & _BOR40V'                          DEFINES & INCLUDES
' ================================================================
 DEFINE OSC 8
'                REGISTERS AND PINOUT ( 1 = IN; 0 = OUT )
' ================================================================
           '76543210          '76543210
 TRISA   = %00000000: PORTA = %00000000 
 TRISB   = %00000000: PORTB = %00000000
 TRISC   = %00010000: PORTC = %00000000
 TRISD   = %00000000: PORTD = %00000000
 TRISE   = %00000000: PORTE = %00000000
 ADCON0  = %00000000
 ADCON1  = %00000000
 ANSEL   = %00000000 
 ANSELH  = %00000000
 CM1CON0 = %00000000
 CM2CON0 = %00000000
 SSPSTAT = %00000000  'Configures the SPI Module ( Read DataSheet ) 
 SSPCON  = %00110000  'Configures the SPI Module ( Read DataSheet ) 
 
'                         ALIAS & MODIFIERS
' ================================================================
  nCS VAR PORTA.2 
 nRST VAR PORTA.3
 SCLK VAR PORTC.3
  SDI VAR PORTC.4
  SDO VAR PORTC.5
  
'                        VARIABLES & COSTANTS
' ================================================================
 MCPWRT CON $40    'Command o write in MCP23S17 Address $00
 MCPRED CON $41    'Command o read from MCP23S17 Address $00
 IOCON  CON $0A    'Register address to MCP23S17 Config
 IODIRA CON $00    'Register address to MCP23S17 PortA(1)
 IODIRB CON $01    'Register address to MCP23S17 PortB(2)
 GPIOA  CON $12    'Register address to MCP23S17 GPIOA(1)
 GPIOB  CON $13    'Register address to MCP23S17 GPIOB(2)
 OLATA  CON $14    'Register address to MCP23S17 LATA(1)
 OLATB  CON $15    'Register address to MCP23S17 LATB(2)
  
 DataOut VAR BYTE  'Variable for Data Byte to Send to the MCP23S17
 DataIn  VAR BYTE  'Variable for Data Byte to Receive from the MCP23S17
 MCPReg  VAR BYTE  'Variable for the Register to Send to the MCP23S17
 
'                           PROGRAM INIT
' ================================================================
    GOSUB INIT_MCP23S17    'Init the MCP23S17
'                            MAIN LOOP
' ================================================================
MAIN:
    MCPReg=OLATA             'This light up the leds, connected in
    DataOut=DataOut+1        'PortA(1) of the MCP23S17
    GOSUB SEND_MCP23S17
    
    MCPReg = GPIOB           'This read the PortB(1) of the MCP23S17
    GOSUB RECEIVE_MCP23S17   'and show the result on the PORTB of the
    PORTB = DataIn           'PIC
    
    PAUSE 200
GOTO MAIN
'                              SUB - ROTINES
' ================================================================    
INIT_MCP23S17:
    nRST = 0                'Reset the port expander
    PAUSE 1
    nRST = 1
    MCPReg = IOCON          'Configures the MCP23S17
    DataOut = $20
    GOSUB SEND_MCP23S17
    MCPReg = IODIRA         'Configures PortA(1) All Output
    DataOut = $00
    GOSUB SEND_MCP23S17
    
    MCPReg = IODIRB         'Configures PortB(2) All Input
    DataOut = $FF
    GOSUB SEND_MCP23S17      
RETURN
SEND_MCP23S17:
    nCS = 0                 'Enable the MCP23S17
    SSPBUF = MCPWRT         'Command to Write to the MCP23S17
    PAUSEUS 1    
    SSPBUF = MCPReg         'Register to Write the Data
    PAUSEUS 1 
    SSPBUF = DataOut        'Data to be sent
    PAUSEUS 1           
    nCS = 1                 'Disable the MCP23S17
RETURN
RECEIVE_MCP23S17:
    nCS = 0                 'Enable the MCP23S17
    SSPBUF = MCPRED         'Command to Read from the MCP23S17
    PAUSEUS 1 
    SSPBUF = MCPReg         'Register to Read from
    PAUSEUS 1  
    SSPBUF = 0              'Send something
    PAUSEUS 1  
    DataIn = SSPBUF         'Data received from te MCP23S17
    PAUSEUS 1 
    nCS = 1                 'Disable the MCP23S17
RETURN
END

Size: 166 Words

Time to execute the following Routine ( Send) - 92 ticks -> 46.0uS

Code:

    MCPReg=OLATA             'This light up the leds, connected in
    DataOut=DataOut+1        'PortA(1) of the MCP23S17
    GOSUB SEND_MCP23S17

Time to execute the following Routine ( Receive) - 119 ticks -> 59.1uS

Code:

    MCPReg = GPIOB           'This read the PortB(1) of the MCP23S17
    GOSUB RECEIVE_MCP23S17   'and show the result on the PORTB of the
    PORTB = DataIn           'PIC

**gadelhas** · - 1st February 2012, 19:53

Code:

'****************************************************************
'*  Name    : MCP23S17 + MSPP + ASM                             *
'*  Author  : [GADELHAS]                                        *
'*  Notice  : Copyright (c) 2012                                *
'*          : All Rights Reserved                               *
'*  Date    : 31-01-2012                                        *
'*  Version : 1.0                                               *
'*  Notes   :                                                   *
'*          : EASYPICV6 + PIC16F887 + MCP23S17                  *
'****************************************************************
'                              CONFIGS
' ================================================================
@ __CONFIG _CONFIG1, _HS_OSC & _WDT_OFF & _PWRTE_OFF & _MCLRE_ON & _CP_OFF & _BOR_OFF & _DEBUG_OFF & _LVP_OFF & _FCMEN_ON & _IESO_OFF  
@ __CONFIG _CONFIG2, _WRT_OFF & _BOR40V
'                          DEFINES & INCLUDES
' ================================================================
 DEFINE OSC 8
'                REGISTERS AND PINOUT ( 1 = IN; 0 = OUT )
' ================================================================
           '76543210          '76543210
 TRISA   = %00000000: PORTA = %00000100 
 TRISB   = %00000000: PORTB = %00000000
 TRISC   = %00010000: PORTC = %00000000
 TRISD   = %00000000: PORTD = %00000000
 TRISE   = %00000000: PORTE = %00000000
 ADCON0  = %00000000
 ADCON1  = %00000000
 ANSEL   = %00000000 
 ANSELH  = %00000000
 CM1CON0 = %00000000
 CM2CON0 = %00000000
 SSPSTAT = %00000000  'Configures the SPI Module ( Read DataSheet ) 
 SSPCON  = %00110000  'Configures the SPI Module ( Read DataSheet ) 
 
'                         ALIAS & MODIFIERS
' ================================================================
  nCS VAR PORTA.2 
 nRST VAR PORTA.3
 SCLK VAR PORTC.3
  SDI VAR PORTC.4
  SDO VAR PORTC.5
  
'                        VARIABLES & COSTANTS
' ================================================================
 MCPWRT CON $40    'Command o write in MCP23S17 Address $00
 MCPRED CON $41    'Command o read from MCP23S17 Address $00
 IOCON  CON $0A    'Register address to MCP23S17 Config
 IODIRA CON $00    'Register address to MCP23S17 PortA(1)
 IODIRB CON $01    'Register address to MCP23S17 PortB(2)
 GPIOA  CON $12    'Register address to MCP23S17 GPIOA(1)
 GPIOB  CON $13    'Register address to MCP23S17 GPIOB(2)
 OLATA  CON $14    'Register address to MCP23S17 LATA(1)
 OLATB  CON $15    'Register address to MCP23S17 LATB(2)
 
 DataOut VAR BYTE  'Variable for Data Byte to Send to the MCP23S17
 DataIn  VAR BYTE  'Variable for Data Byte to Receive from the MCP23S17
 MCPReg  VAR BYTE  'Variable for the Register to Send to the MCP23S17
 
'                           PROGRAM INIT
' ================================================================
    GOSUB INIT_MCP23S17    'Init the MCP23S17
'                            MAIN LOOP
' ================================================================
MAIN:
    MCPReg=OLATA             'This light up the leds, connected in
    DataOut=DataOut+1        'PortA(1) of the MCP23S17
    GOSUB SEND_MCP23S17
    
    MCPReg = GPIOB           'This read the PortB(1) of the MCP23S17
    GOSUB RECEIVE_MCP23S17   'and show the result on the PORTB of the
    PORTB = DataIn           'PIC
    
    PAUSE 200
GOTO MAIN
'                              SUB - ROTINES
' ================================================================    
INIT_MCP23S17:
    nRST = 0                'Reset the port expander
    PAUSE 1
    nRST = 1
    MCPReg = IOCON          'Configures the MCP23S17
    DataOut = $20
    GOSUB SEND_MCP23S17
    MCPReg = IODIRA         'Configures PortA(1) All Output
    DataOut = $00
    GOSUB SEND_MCP23S17
    
    MCPReg = IODIRB         'Configures PortB(2) All Input
    DataOut = $FF
    GOSUB SEND_MCP23S17      
RETURN
SEND_MCP23S17:  
ASM
 bcf PORTA, 2               ;Enable the MCP23S17
 MOVE?CB _MCPWRT, SSPBUF    ;Command to Write to the MCP23S17
 call _delay
 MOVE?BB _MCPReg, SSPBUF    ;Register to Write the Data
 call _delay
 MOVE?BB _DataOut, SSPBUF   ;Data to be sent
 call _delay                
 bsf PORTA, 2               ;Disable the MCP23S17
ENDASM
RETURN
RECEIVE_MCP23S17:
ASM
 bcf PORTA, 2               ;Enable the MCP23S17
 MOVE?CB _MCPRED, SSPBUF    ;Command to Read from the MCP23S17
 call _delay
 MOVE?BB _MCPReg, SSPBUF    ;Register to Read from
 call _delay
 MOVE?BB _DataOut, SSPBUF   ;Send something
 call _delay 
 MOVE?BB SSPBUF, _DataIn    ;Data received from te MCP23S17
 bsf PORTA, 2               ;Disable the MCP23S17
ENDASM
RETURN
delay:                      'Delay Routine 3uS - You may have to change if running OSC faster  
asm                         ;8Mhz/4 = 2Mhz = 0.5uS X 6cycles(2 p/goto) = 3uS
 goto $+1
 goto $+1
 goto $+1
endasm
return
END

Size: 157 Words

Time to execute the following Routine ( Send) - 47 ticks -> 23.1uS

Code:

    MCPReg=OLATA             'This light up the leds, connected in
    DataOut=DataOut+1        'PortA(1) of the MCP23S17
    GOSUB SEND_MCP23S17

Time to execute the following Routine ( Receive) - 50 ticks -> 25.0uS

Code:

    MCPReg = GPIOB           'This read the PortB(1) of the MCP23S17
    GOSUB RECEIVE_MCP23S17   'and show the result on the PORTB of the
    PORTB = DataIn           'PIC

**Demon** · - 2nd February 2012, 02:31

This is great stuff. I use the MCP23016, but this new IC is much faster.

Can you explain how you came up with the 3us delay in the 3rd approach? I look at your comment and the SPI characteristics in the datasheet and don't know what to use exactly.

Robert

**gadelhas** · - 2nd February 2012, 13:48

Originally Posted by Demon

This is great stuff. I use the MCP23016, but this new IC is much faster.

Can you explain how you came up with the 3us delay in the 3rd approach? I look at your comment and the SPI characteristics in the datasheet and don't know what to use exactly.

Robert

Hi Robert, Thanks for your comment.

Hi came up with 3 uS by trial and error. I tried 2 uS, but it wasn´t enough. The problem is not the MCP23S17, but the SSPUBUF register of the PIC. I think if you run the PIC faster, for instance @20Mhz, you can even reduce that time.

**Demon** · - 2nd February 2012, 23:30

Wouldn't it be the other way around? If you run a PIC faster, it would cycle quicker so you'd need more delay instructions no?

I checked the datasheet again and page 35 table 2-4 has 500ns for Serial Data to Output Valid. Does that mean it takes 500ns for the IC to process a complete output operation?

I would assume reading is quicker...?

Robert

**gadelhas** · - 3rd February 2012, 00:28

Originally Posted by Demon

Wouldn't it be the other way around? If you run a PIC faster, it would cycle quicker so you'd need more delay instructions no?

I checked the datasheet again and page 35 table 2-4 has 500ns for Serial Data to Output Valid. Does that mean it takes 500ns for the IC to process a complete output operation?

I would assume reading is quicker...?

Robert

The problem is that when you put a byte in the SSPUF of the PIC, it takes some time for the PIC to output that byte( @8Mhz ~3uS ). If you run the PIC faster, the time that it takes to output the byte gets reduced.
At this speed ( 8Mhz ), you put the byte into the SSPUF and you must wait 3us to put another byte in the SSPUF, if you put a byte before the 3us, for instance at 2us, the byte before will be corrupted and the pic will output the new byte and miss the byte before. You can try this in the simulation that is attached.

You are looking at the wrong table ( 2-4 GP and INT TIMMING). You should look table 2-3 (SPI Characteristics ). The MCP23S17 can RUN at a max of 10Mhz ( SPI ).

**HenrikOlsson** · - 3rd February 2012, 07:54

Hi,
Instead of relying on software timing you can check the MSSP interrupt flag:

Code:

myByte VAR BYTE
SSPIF VAR PIR1.3

myByte = 123

SSPBUF = myByte                 ' Load byte to shiftregister buffer
SSPIF = 0                             ' Clear interrupt flag
WHILE SSPIF=0 : WEND        ' Wait for transmission to finish

This way you don't have to change any timing if you change the oscillator or if you change the MSSP module clock divisor etc.

Check the datasheet and make sure the SSPIF is at PIR1.3 for your device. (I think they try to keep it consistent but you never know)

/Henrik.

Thread: MCP23S17 - Three different approaches - ShiftIn/ShiftOut / MSSP+PBP / MSSP+ASM

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