Hi,
I'm building a circuit which consists of a PIC 18F2550, a 16 bit ADC (Microchip's MCP3426) and an LCD to display the ADC's readings.
The LCD I managed to get it working and developed a couple of routines for it, thats not really the problem now.
My problem is in getting a reading from the ADC via I2C.
Since I have never used I2C before, I looked for help and managed to find **broken link removed**. Using these routines, I found a bit of a problem on the byte write routine.
First I have to send a byte to the MCP, that first byte is composed of:
bits 7-4: Device Code: 1101
bits 3-1: Address bits: thats the problem...
bit 0: Read/Write' bit
After that byte, the byte I send is considered to be the configuration register.
When I say the address bits are the problem it is because nowhere in the datasheet it gives me an exact address for this device. The MCP3427 and 3428 have a table, but for the 3426 it just says it is "programmed at the factory during production". So what am I supposed to do? I tried sending 000, but apparently that didn't work.
Anyone has any clue?
I'm posting the circuit. The I2C code from AN989 (changed a little for my purposes -- so far I have only tried to use routines Init, ByteWrite and ByteRead) is:
I'm building a circuit which consists of a PIC 18F2550, a 16 bit ADC (Microchip's MCP3426) and an LCD to display the ADC's readings.
The LCD I managed to get it working and developed a couple of routines for it, thats not really the problem now.
My problem is in getting a reading from the ADC via I2C.
Since I have never used I2C before, I looked for help and managed to find **broken link removed**. Using these routines, I found a bit of a problem on the byte write routine.
First I have to send a byte to the MCP, that first byte is composed of:
bits 7-4: Device Code: 1101
bits 3-1: Address bits: thats the problem...
bit 0: Read/Write' bit
After that byte, the byte I send is considered to be the configuration register.
When I say the address bits are the problem it is because nowhere in the datasheet it gives me an exact address for this device. The MCP3427 and 3428 have a table, but for the 3426 it just says it is "programmed at the factory during production". So what am I supposed to do? I tried sending 000, but apparently that didn't work.
Anyone has any clue?
I'm posting the circuit. The I2C code from AN989 (changed a little for my purposes -- so far I have only tried to use routines Init, ByteWrite and ByteRead) is:
Code:
;*******************Initialization subroutine*********************
; This routine initializes the MSSP module
; for I2C Master mode, with a 100 kHz clock.
;*****************************************************************
Init
movlw b'11111111'
movwf TRISB ; Set PORTB to all inputs
clrf SSPSTAT ; Disable SMBus inputs
bsf SSPSTAT,SMP ; Disable slew rate control
movlw 0x18 ; Load 0x18 into WREG
movwf SSPADD ; Setup 100 kHz I2C clock
movlw b'00101000'
movwf SSPCON1 ; Enable SSP, select I2C Master mode
clrf SSPCON2 ; Clear control bits
bcf PIR1,SSPIF ; Clear SSP interrupt flag
bcf PIR2,BCLIF ; Clear Bit Collision flag
return
;*******************Start bit subroutine**************************
; This routine generates a Start condition
; (high-to-low transition of SDA while SCL
; is still high.
;*****************************************************************
BSTART
bcf PIR1,SSPIF ; Clear SSP interrupt flag
bsf SSPCON2,SEN ; Generate Start condition
bstart_wait
btfss PIR1,SSPIF ; Check if operation completed
bra bstart_wait ; If not, keep checking
return
;*******************Restart bit subroutine**************************
; This routine generates a Repeated Start
; condition (high-to-low transition of SDA
; while SCL is still high.
;*****************************************************************
BRESTART
bcf PIR1,SSPIF ; Clear SSP interrupt flag
bsf SSPCON2,RSEN ; Generate Restart condition
brestart_wait
btfss PIR1,SSPIF ; Check if operation completed
bra brestart_wait ; If not, keep checking
return
;*******************Stop bit subroutine***************************
; This routine generates a Stop condition
; (low-to-high transition of SDA while SCL
; is still high.
;*****************************************************************
BSTOP
bcf PIR1,SSPIF ; Clear SSP interrupt flag
bsf SSPCON2,PEN ; Generate Stop condition
bstop_wait
btfss PIR1,SSPIF ; Check if operation completed
bra bstop_wait ; If not, keep checking
return
;*******************Data transmit subroutine**********************
; This routine transmits the byte of data
; stored in 'datao' to the serial EEPROM
; device. Instructions are also in place
; to check for an ACK bit, if desired.
; Just replace the 'bra' instruction,
; or create an 'ackfailed' label, to provide
; the functionality.
;*****************************************************************
TX_BYTE
bcf PIR1,SSPIF ; Clear SSP interrupt flag
movf datao,W ; Copy datao to WREG
movwf SSPBUF ; Write byte out to device
tx_wait
btfss PIR1,SSPIF ; Check if operation completed
bra tx_wait ; If not, keep checking
btfsc SSPCON2,ACKSTAT ; Check if ACK bit was received
call ackfailed ; This executes if no ACK received
return
;*******************Data receive subroutine***********************
; This routine reads in one byte of data from
; the serial EEPROM device, and stores it in
; 'datai'. It then responds with either an
; ACK or a NO ACK bit, depending on the value
; of 'ACKDT' in 'SSPCON2'.
;*****************************************************************
RX_BYTE
bcf PIR1,SSPIF ; Clear SSP interrupt flag
bsf SSPCON2,RCEN ; Initiate reception of byte
rx_wait
btfss PIR1,SSPIF ; Check if operation completed
bra rx_wait ; If not, keep checking
movf SSPBUF,W ; Copy byte to WREG
movwf datai ; Copy WREG to datai
bcf PIR1,SSPIF ; Clear SSP interrupt flag
bsf SSPCON2,ACKEN ; Generate ACK/NO ACK bit
rx_wait2
btfss PIR1,SSPIF ; Check if operation completed
bra rx_wait2 ; If not, keep checking
return
;*******************Byte write test subroutine********************
; This routine tests the byte write feature
; of the serial EEPROM device. It will write
; 1 byte of data to the device at address 0x5A00.
;*****************************************************************
ByteWrite
rcall BSTART ; Generate Start condition
; Send control byte
movlw WRITE_ADDR ; Load control byte for write
movwf datao ; Copy to datao for output
rcall TX_BYTE ; Send control byte to device
; Send word address high byte
movlw B'10011000' ; Configuração do MCP!!!
movwf datao ; Copy to datao for output
rcall TX_BYTE
rcall BSTOP ; Generate Stop condition
; rcall Poll ; Poll for write completion
return
;*******************Page write test subroutine********************
; This routine demonstrates the page write
; feature of the serial EEPROM device. It will
; write NUMBYTES number of bytes of data to the
; device starting at address 0x5A00. Since this
; is a page write, all bytes will be written
; to the device at the same time.
; Note that if a page boundary is crossed during
; the operation, the address will wrap back to
; the beginning of the page, overwriting any
; previously stored data.
;*****************************************************************
PageWrite
movlw NUMBYTES
movwf bytecount ; Initialize counter to NUMBYTES
rcall BSTART ; Generate start bit
; Now we send the control byte
movlw WRITE_ADDR
movwf datao ; Copy control byte to buffer
rcall TX_BYTE ; Output control byte to device
; Send word address high byte
movlw 0x5A ; Use 0x5A for address to send
movwf datao ; Copy address to buffer
rcall TX_BYTE
; Send word address low byte
movlw 0x00 ; Use 0x00 for address to send
movwf datao ; Copy address to buffer
rcall TX_BYTE ; Output address to device
txbyte ; This loop transfers all of
; the data bytes to the device
movf bytecount,W ; Use bytecount as data value
movwf datao ; Copy data to buffer
rcall TX_BYTE ; Output data to device
decfsz bytecount,F ; Check if finished looping
bra txbyte ; Continue looping
rcall BSTOP ; Generate stop bit
rcall Poll ; Poll for write completion
return
;*******************Byte read test subroutine*********************
; This routine tests the byte read feature
; of the serial EEPROM device. It will read
; 1 byte of data at address 0x5A00 from the device.
;*****************************************************************
ByteRead
rcall BSTART ; Generate Start condition
; ; Send control byte
; movlw WRITE_ADDR ; Load control byte for write
; movwf datao ; Copy to datao for output
; rcall TX_BYTE ; Send control byte to device
;
; ; Send word address high byte
; movlw 0x5A ; Load 0x5A for word address
; movwf datao ; Copy to datao for output
; rcall TX_BYTE ; Send high byte to device
;
; ; Send word address low byte
; movlw 0x00 ; Load 0x00 for word address
; movwf datao ; Copy to datao for output
; rcall TX_BYTE ; Send word address to device
;
; rcall BRESTART ; Generate Restart condition
; Send control byte
movlw READ_ADDR ; Load control byte for read
movwf datao ; Copy to datao for output
rcall TX_BYTE ; Send control byte to device
; Read data byte
bsf SSPCON2,ACKDT ; Select to send NO ACK bit
rcall RX_BYTE ; Read data byte from device
rcall BSTOP ; Generate Stop condition
return
;*******************Sequential read test subroutine***************
; This routine tests the sequential read feature
; of the serial EEPROM device. It will read
; NUMBYTES number of bytes of data to the device
; starting at address 0x5A00, one byte after another.
;*****************************************************************
SequentialRead
movlw NUMBYTES
movwf bytecount ; Initialize counter to NUMBYTES
rcall BSTART ; Generate start bit
; Now send the control byte
; for a write, to set address
movlw WRITE_ADDR
movwf datao ; Copy control byte to buffer
rcall TX_BYTE ; Output control byte to device
; Send word address high byte
movlw 0x5A ; Load 0x5A for word address
movwf datao ; Copy to datao for output
rcall TX_BYTE ; Send high byte to device
; Send word address low byte
movlw 0x00 ; Load 0x5A for word address
movwf datao ; Copy to datao for output
rcall TX_BYTE ; Send word address to device
rcall BRESTART ; Generate another start bit
; to switch to read mode
movlw READ_ADDR
movwf datao ; Copy control byte to buffer
rcall TX_BYTE ; Output control byte to device
rxbyte
; Finally, read the data byte
decfsz bytecount,F ; Check if finished looping
bra continue ; If not finished, keep going
bsf SSPCON2,ACKDT ; Otherwise, select to send NO ACK bit
rcall RX_BYTE ; and input final byte from device
rcall BSTOP ; Generate stop bit
return
continue
bcf SSPCON2,ACKDT ; Select to send ACK bit
rcall RX_BYTE ; Input data from device
bra rxbyte ; Continue looping
;*******************Acknowledge Polling subroutine****************
; This subroutine polls the EEPROM device
; for an ACK bit, which indicates that the
; internal write cycle has completed. Code
; is in place for a timeout routine, just
; uncomment the 'bra TimedOut' line, and
; provide a 'TimedOut' label.
;*****************************************************************
Poll
movlw .40
movwf pollcnt ; Set max polling times to 40
polling
rcall BRESTART ; Generate start bit
movlw WRITE_ADDR ; Now send the control byte
movwf datao ; Copy control byte to buffer
rcall TX_BYTE ; Output control byte to device
btfss SSPCON2,ACKSTAT ; Was the ACK bit low?
bra exitpoll ; If yes, stop polling
; If no, check if polled 40 times
decfsz pollcnt,F ; Is poll counter down to zero?
bra polling ; If no, poll again
; bra TimedOut ; If yes, part didn't respond
; in time, so take action
exitpoll
rcall BSTOP ; Generate stop bit
return
