- Blog entry posted in 'Electronics and Other Ramblings...', March 13, 2012.
I2C Monitor– Implementation and Limitations
The implementation is shown on the next figure. For the quick prototype, the FTDI interface was replaced with the FTDI TTL cable. The implementation worked as expected with two caveats; the maximum bus supported speed is 100kHz, and if the internal buffer on the MCU overflows there is currently no indication for this. I was hoping to be able to operate up to 400kHz, but it’s not happening. Since this is good enough for what I targeted originally, it will suffice until next time. It looks like this is better suited for an FPGA application – live and learn I guess. Code is written in Oshonsoft Basic.
70235
Code
Code:
'Author: languer (©2012)
'Pin Allocation:
'PIN# Main_Fn Secondary_Fn
'RA0 -> not used
'RA1 -> not used
'RA2 -> not used
'RA3 -> not used
'RA4 -> not used
'RA5 -> MCLR
'RA6 -> OSC
'RA7 -> OSC
'RB0 -> I2C START Interrupt
'RB1 -> TX_RS232 (PC_RX)
'RB2 -> I2C STOP Interrupt
'RB3 -> I2C SCL Interrupt (using CCP)
'RB4 -> RX_RS232 (PC_TX)
'RB5 -> not used
'RB6 -> I2C SDA PGC (Programming clock)
'RB7 -> CTS# PGD (Programming data)
'Usage Information:
'RS232 Baud Rate: 115.2kbps
'Version Info:
'rs232 comms on array at main loop
'max speed is 100kHz
'no indication if buffer overflows
'General Configuration
'for external 10MHz w PLL (40MHz)
Define CONFIG1L = 0x00
Define CONFIG1H = 0x06
Define CONFIG2L = 0x0a
Define CONFIG2H = 0x00
Define CONFIG3L = 0x00
Define CONFIG3H = 0x80
Define CONFIG4L = 0x80
Define CONFIG4H = 0x00
Define CONFIG5L = 0x03
Define CONFIG5H = 0xc0
Define CONFIG6L = 0x03
Define CONFIG6H = 0xe0
Define CONFIG7L = 0x03
Define CONFIG7H = 0x40
'Oscillator/Clock Configuration
Define CLOCK_FREQUENCY = 40
'HW UART Setup
Hseropen 115200
'I2C Definitions
Symbol io_i2cstart = RB0
Symbol io_i2cstop = RB2
Symbol io_i2cscl = RB3
Symbol io_i2csda = RB6
'Constants
Const trisa1 = %11111111
Const trisb1 = %01111101
Dim _true As Bit
Dim _false As Bit
_true = True
_false = False
'Variables
Dim flag_i2cstart As Bit
Dim flag_i2cstop As Bit
Dim i2cack As Byte
Dim i2cdata As Byte
Const i2cbuffersize = 200
Dim i2carray(200) As Byte
Dim i2cnextin As Byte
Dim i2cnextout As Byte
Dim bitcount As Byte
'Main Program
main:
WaitMs 2500
Call init()
'enable interrupt routines
INTCON.INT0IE = True 'enable RB0/I2CSTART interrupt
CCP1CON = %00000101 'enable RB3/CCP1/I2CSCL
Enable High 'enable general interrupt
Dim data As Byte
Dim cnt As Byte
While _true
If i2cnextout = i2cnextin Then
'do nothing
Else
'loop-around buffer
If i2cnextout = i2cbuffersize Then
i2cnextout = 0
Endif
'hserout when TXREG is empty
If PIR1.TXIF = True Then
data = i2carray(i2cnextout)
TXREG = data
i2cnextout = i2cnextout + 1
Endif
Endif
Wend
End
Proc init()
AllDigital
TRISA = trisa1
TRISB = trisb1
flag_i2cstart = False
flag_i2cstop = False
i2cack = 0
i2cdata = 255
i2cnextin = 0
i2cnextout = 0
bitcount = 0
'Hserout "Start...", CrLf
End Proc
On High Interrupt
Dim hex1 As Byte
Dim hex2 As Byte
'START/RESTART Condition (3.6us / 29Tcy)
If INTCON.INT0IF = True Then 'RB0/I2CSTART flag
INTCON.INT0IF = False 'RB0/I2CSTART flag
INTCON3.INT2IF = False 'RB2/I2CSTOP flag
INTCON3.INT2IE = True 'enable RB2/I2CSTOP interrupt
flag_i2cstop = False
bitcount = 0
PIR1.CCP1IF = False 'RB3/CCP/I2CSCL flag
PIE1.CCP1IE = True 'enable RB3/CCP/I2CSCL interrupt
INTCON.PEIE = True 'enable peripheral interrupt (required for RB3/CCP/I2CSCL)
'loop-around buffer
If i2cnextin = i2cbuffersize Then
i2cnextin = 0
Endif
If flag_i2cstart = True Then
i2carray(i2cnextin) = "R" 'restart condition"
Else
flag_i2cstart = True
i2carray(i2cnextin) = "S" 'start condition
Endif
i2cnextin = i2cnextin + 1
Endif
'STOP Condition (3.0us / 24Tcy)
If INTCON3.INT2IF = True Then 'RB2/I2CSTOP flag
INTCON3.INT2IE = False 'disable RB2/I2CSTOP interrupt
INTCON3.INT2IF = False 'RB2/I2CSTOP flag
INTCON.PEIE = False 'disable peripheral interrupt (required for RB3/CCP/I2CSCL)
PIE1.CCP1IE = False 'disable RB3/CCP/I2CSCL interrupt
PIR1.CCP1IF = False 'RB3/CCP/I2CSCL flag
flag_i2cstart = False
'loop-around buffer
If i2cnextin = i2cbuffersize Then
i2cnextin = 0
Endif
i2carray(i2cnextin) = "P" 'stop condition
i2cnextin = i2cnextin + 1
Endif
'DATA Condition
'(2.4us / 18Tcy for Bits 0-6)
'(7.2us / 55Tcy for Bit 7)
'(7.4us / 58Tcy for ACK/NACK)
If PIR1.CCP1IF = True Then 'RB3/CCP/I2CSCL flag
PIR1.CCP1IF = False 'RB3/CCP/I2CSCL flag
Select Case bitcount
Case < 7
'shift data left and add new i2cdata bit
'i2cdata = ShiftLeft(i2cdata, 1)
ASM: RLCF i2cdata,1
If io_i2csda = True Then 'add
i2cdata = i2cdata + 1
Endif
bitcount = bitcount + 1
Case 7
'shift data left and add last i2cdata bit
'i2cdata = ShiftLeft(i2cdata, 1)
ASM: RLCF i2cdata,1
If io_i2csda = True Then 'add
i2cdata = i2cdata + 1
Endif
bitcount = bitcount + 1
'store I2CDATA
'loop-around buffer
'hex1 = ShiftRight(i2cdata, 4)
ASM: movff i2cdata,hex1
ASM: movf hex1,w
ASM: andlw 0xf0
ASM: movwf hex1
ASM: RRNCF hex1,1
ASM: RRNCF hex1,1
ASM: RRNCF hex1,1
ASM: RRNCF hex1,1
hex1 = LookUp("0123456789ABDCEF"), hex1
'hex2 = i2cdata And 0x0f
ASM: movff i2cdata,hex2
ASM: movlw 0x0f
ASM: andwf hex2,1
hex2 = LookUp("0123456789ABDCEF"), hex2
Case Else
'ACK/NACK bit
If i2cnextin = i2cbuffersize Then
i2cnextin = 0
Endif
i2carray(i2cnextin) = hex1
i2cnextin = i2cnextin + 1
If i2cnextin = i2cbuffersize Then
i2cnextin = 0
Endif
i2carray(i2cnextin) = hex2
i2cnextin = i2cnextin + 1
bitcount = 0
'store ack/nack STATUS
If io_i2csda = True Then 'test for ACK/NACK
i2cack = "A"
Else
i2cack = "N"
Endif
'loop - around buffer
If i2cnextin = i2cbuffersize Then
i2cnextin = 0
Endif
i2carray(i2cnextin) = i2cack
i2cnextin = i2cnextin + 1
EndSelect
Endif
Resume
