Hi there,
I am currently trying to connect up a 24C16 EEPROM to a 16C74 in a
project I am building. I have been trying to find information on how to
connect up this chip but have had little luck. The only thing I found was
a data sheet on the chip by National Semi.. Judging by the data sheet I
came up with the following connections.
_________ __________
| | | |1 A0 NC
| 74 | sclk 6| EE |2 A1 NC
| |18----------| |3 A2 NC
| | | |
| | sda 5| |4 VSS
| |23----------| |
| | | |5 VDD
| | | |
--------- ----------
A0 |
A1 |----- Device Address inputs datasheet gives value as X for 24C16
A2 |
VSS - GND
VDD - +5
pin 6 SCL Clock
pin 5 SDA Data
The software I am using is the example given with the PICDEM board..
which is supposed to work with 24CXX range ?? My problem is my program
never leaves the errorstate loop.. Its exactly as if my EEPROM isn't
there. Personally I think that it may be the Slave address line in the
code.. But I can find no infomation on how this is calculated! or how I
set my EEPROM to match it ?
I'm enclosing the entire code( the only change I made is swaping
each reference to PORTB with PORTD. I doubt if that could be the problem??
Anyway my appologies if this code is a bit much to be enclosing but at the
moment I'm getting pretty desperate and I couldn't isolate the problem to
any section of the code. My project deadline is VERY soon..
Thanks
David.
The CODE :
TITLE "I2C interface PIC16C74 to serial EEPROM"
;
LIST P=16C74, F=INHX8M
;
;*****************************************************************************
;** Two wire/I2C Bus READ/WRITE Sample Routines of Microchip's
;** 24Cxx / 85Cxx serial CMOS EEPROM interfacing to a
;** PIC16C74 8-bit CMOS single chip microcomputer
;** Revised Version (3/1/94).
;**
;** Note: 1) All timing is based on a reference crystal frequency of
4MHz
;** which is equivalent to an instruction cycle time of 1 usec.
;** 2) Address and literal values are read in hexidecimal unless
;** otherwise specified.
;*****************************************************************************
;
;-----------------------------------------------------------------------------
; Register File Assignment
;-----------------------------------------------------------------------------
;
include "picreg.equ"
;
FLAG equ 20 ; Common flag bits register
EEPROM equ 21 ; Bit buffer
ERCODE equ 22 ; Error code (to indicate bus status)
ADDR equ 23 ; Address register
DATAI equ 24 ; Stored data input register
DATAO equ 25 ; Stored data output register
SLAVE equ 26 ; Device address (1010xxx0)
TXBUF equ 27 ; TX buffer
RXBUF equ 28 ; RX buffer
COUNT equ 29 ; Bit counter
TEMP equ 2A ; Temporary storage
TEMP1 equ 2B ; More Temporary storage
;
;-----------------------------------------------------------------------------
; Bit Assignments
;-----------------------------------------------------------------------------
;
; FLAG Bits
;
ERRORFLG EQU 0 ; Error flag
;
; EEPROM Bits
;
DI EQU 7 ; EEPROM input
DO EQU 6 ; EEPROM output
;
; I2C Device Bits
;
SDA EQU 4 ; RB7, data in/out
SCL EQU 3 ; RB6, serial clock
;------------------------------------------------------------------------------
; Vector Assignment
;------------------------------------------------------------------------------
ORG 00h ; Reset Vector
goto Start
;
ORG 04h ; Interrupt Vector
goto Service_int ; Not actually used by this program
;
ORG 10h ; Begining of Program space
;------------------------------------------------------------------------------
; Main Program
;------------------------------------------------------------------------------
Start
clrf FLAG
clrf ERCODE
bsf STATUS,RP0 ; Select Page 1
clrf TRIS_D ; Set PORT_D as all outputs
movlw 0FFh ; Set PORT_C as all inputs
movwf TRIS_C
bcf STATUS,RP0 ; Select Page 0
movlw 01h
movwf PORT_D ; Light first LED
movlw B'00111011' ; I2C master mode enabled
movwf SSPCON
movlw B'00000000' ; Disable interrupts
movwf INTCON
movlw B'00000000' ; Disable all interrupts
movwf PIE1
clrf PORT_C ; Set SCL, SDA to low when not in
tri-state
Bigloop
movf PORT_D,W
movwf DATAO ; Output Data
movlw 00h ; EEPROM data address
movwf ADDR
movlw B'10100000' ; EEPROM I2C address
movwf SLAVE
Wrtloop
call WRBYTE ; Output byte to EEPROM
btfsc FLAG,ERRORFLG ; Check for error
goto Errorloop
call Delay ; 10mS Delay for 24LC01 EEPROM write delay
incf ADDR ; Point to next address
btfss ADDR,7 ; Check if at end of EEPROM
goto Wrtloop
bcf STATUS,RP0 ; Address page 1
movlw 00h ; EEPROM data address
movwf ADDR
movlw B'10100000' ; EEPROM I2C address
movwf SLAVE
Rdloop
call RDBYTE ; Input byte from EEPROM
btfsc FLAG,ERRORFLG ; Check for error
goto Errorloop
movf DATAI,W ; Get received byte
subwf PORT_D,W ; Make sure correct data read
btfss STATUS,Z
goto Errorloop
incf ADDR ; Point to next address
btfss ADDR,7 ; Check if at end of EEPROM
goto Rdloop
incf PORT_D ; Increment value displayed on LEDs
goto Bigloop
Errorloop
clrf PORT_D ; Turn off all LEDs
Errloop1
call Delay ; Delay so that flashing of LEDs
call Delay ; is apparent
call Delay
call Delay
call Delay
call Delay
comf PORT_D ; Change state of all LEDs
goto Errloop1
Service_int ; Interrupts are not used
return
;-----------------------------------------------------------------------------
; BYTE-WRITE, write one byte to EEPROM device
;-----------------------------------------------------------------------------
; Input : DATAO = data to be written
; ADDR = EEPROM data address
; SLAVE = device address (1010xxx0)
; Output : Data written to EEPROM device
;-----------------------------------------------------------------------------
WRBYTE
bcf STATUS,RP0
movf SLAVE,W ; Put SLAVE address
movwf TXBUF ; in xmit buffer
call BSTART ; Generate START bit
call TX ; Output SLAVE address
bcf STATUS,RP0
movf ADDR,W ; Put WORD address
movwf TXBUF ; in xmit buffer
call TX ; Output WORD address
bcf STATUS,RP0
movf DATAO,W ; Move DATA
movwf TXBUF ; into buffer
call TX ; Output DATA and detect acknowledgement
call BSTOP ; Generate STOP bit
return
;-----------------------------------------------------------------------------
; TRANSMIT 8 data bits subroutine
;-----------------------------------------------------------------------------
; Input : TXBUF
; Output : Data transmitted to EEPROM device
;-----------------------------------------------------------------------------
TX
bcf STATUS,RP0
movlw .8 ; Set counter for eight bits
movwf COUNT
TXLP
bcf EEPROM,DO ; Default 0 bit out
btfsc TXBUF,7 ; If shifted bit = 0, data bit = 0
bsf EEPROM,DO ; otherwise data bit = 1
call BITOUT ; Send bit
bcf STATUS,RP0
rlf TXBUF ; Rotate TXBUF left
skpc ; f(6) ---> f(7)
bcf TXBUF,0 ; f(7) ---> carry
skpnc ; carry ---> f(0)
bsf TXBUF,0
decfsz COUNT ; 8 bits done?
goto TXLP ; No.
call BITIN ; Read acknowledge bit
bcf STATUS,RP0
movlw 3
btfsc EEPROM,DI ; Check for acknowledgement
call ERR ; No acknowledge from device
bcf STATUS,RP0
retlw 0
;-----------------------------------------------------------------------------
; Single bit data transmit from PIC to serial EEPROM
;-----------------------------------------------------------------------------
; Input : EEPROM register, bit DO
; Output : Bit transmitted over I2C
; Error bits set as necessary
;-----------------------------------------------------------------------------
BITOUT
btfss EEPROM,DO
goto BIT0
bsf STATUS,RP0
bsf TRIS_C,SDA ; Output bit 0
movlw 2
bcf STATUS,RP0
btfsc PORT_C,SDA ; Check for error code 2
goto CLK1
call ERR
goto CLK1 ; SDA locked low by device
BIT0
bsf STATUS,RP0
bcf TRIS_C,SDA ; Output bit 0
nop ; Delay
CLK1
bsf STATUS,RP0
bsf TRIS_C,SCL ; Attempt to set SCL high
movlw 1 ; Error code 1
bcf STATUS,RP0
btfsc PORT_C,SCL ; SCL locked low?
goto BIT2 ; No.
call ERR ; Yes, set error
BIT2
nop ; Timing delay
nop
bsf STATUS,RP0
bcf TRIS_C,SCL ; Return SCL to low
bcf STATUS,RP0
retlw 0
;-----------------------------------------------------------------------------
; BYTE-READ, read one byte from serial EEPROM device
;-----------------------------------------------------------------------------
; Input : ADDR = source address
; SLAVE = device address (1010xxx0)
; Output : DATAI = data read from serial EEPROM
;-----------------------------------------------------------------------------
;
RDBYTE
bcf STATUS,RP0
movf SLAVE,W ; Move SLAVE address
movwf TXBUF ; into xmit buffer (R/W = 0)
call BSTART ; Generate START bit
call TX ; Output SLAVE address. Check ACK.
bcf STATUS,RP0
movf ADDR,W ; Move WORD address
movwf TXBUF ; into xmit buffer
call TX ; Output WORD address. Check ACK.
call BSTART ; START READ (if only one device is
bcf STATUS,RP0 ; connected to the I2C bus)
movf SLAVE,W
movwf TXBUF
bsf TXBUF,0 ; Specify READ mode (R/W = 1)
call TX ; Output SLAVE address
call RX ; READ in data and acknowledge
call BSTOP ; Generate STOP bit
bcf STATUS,RP0
movf RXBUF,W ; Save data from buffer
movwf DATAI ; to DATAI file register.
return
;
;-----------------------------------------------------------------------------
; RECEIVE eight data bits subroutine
;-----------------------------------------------------------------------------
; Input : None
; Output : RXBUF = 8-bit data received
;-----------------------------------------------------------------------------
;
RX
bcf STATUS,RP0
movlw .8 ; 8 bits of data
movwf COUNT
clrf RXBUF
;
RXLP
rlf RXBUF ; Shift data to buffer
skpc
bcf RXBUF,0 ; carry ---> f(0)
skpnc
bsf RXBUF,0
call BITIN
bcf STATUS,RP0
btfsc EEPROM,DI
bsf RXBUF,0 ; Input bit =1
decfsz COUNT ; 8 bits?
goto RXLP
bsf EEPROM,DO ; Set acknowledge bit = 1
call BITOUT ; to STOP further input
retlw 0
;
;-----------------------------------------------------------------------------
; Single bit receive from serial EEPROM to PIC
;-----------------------------------------------------------------------------
; Input : None
; Output : Data bit received
;-----------------------------------------------------------------------------
;
BITIN
bsf STATUS,RP0
bsf TRIS_C,SDA ; Set SDA for input
bcf STATUS,RP0
bcf EEPROM,DI
bsf STATUS,RP0
bsf TRIS_C,SCL ; Clock high
movlw 1
bcf STATUS,RP0
btfsc PORT_C,SCL ; Skip if SCL is high
goto BIT1
call ERR
BIT1
bcf STATUS,RP0
btfss PORT_C,SDA ; Read SDA pin, for ACK low
goto ACKOK
bsf EEPROM,DI ; DI = 1
ACKOK
bsf STATUS,RP0
nop ; Delay
bcf TRIS_C,SCL ; Return SCL to low
bcf STATUS,RP0
retlw 0
;-----------------------------------------------------------------------------
; DELAY, Provide a 10.78mS delay
;-----------------------------------------------------------------------------
; Input : None
; Output : None
;-----------------------------------------------------------------------------
Delay
bcf STATUS,RP0
movlw 7
movwf TEMP1
clrf TEMP ;clear last location
dly1
nop
nop
nop
decfsz TEMP ;reduce count
goto dly1 ;Inner loop time = 1.54mS
decfsz TEMP1
goto dly1 ;Total time = 10.78mS
retlw 0
;-----------------------------------------------------------------------------
; START bit generation routine
;-----------------------------------------------------------------------------
; input : none
; output : initialize bus communication
;-----------------------------------------------------------------------------
;
;Generate START bit (SCL is high while SDA goes from high to low
transition)
;and check status of the serial clock.
BSTART
bsf STATUS,RP0
bsf TRIS_C,SDA ; Make sure SDA is high
bsf TRIS_C,SCL ; Set clock high
movlw 1 ; Ready error status code 1
bcf STATUS,RP0
btfss PORT_C,SCL ; Locked?
call ERR ; SCL locked low by device, flag error
bsf STATUS,RP0
bcf TRIS_C,SDA ; SDA goes low during SCL high
nop ; Timing adjustment, 1uS @4MHz
bcf TRIS_C,SCL ; Start clock train
bcf STATUS,RP0
RETLW 0
;-----------------------------------------------------------------------------
; STOP bit generation routine
;-----------------------------------------------------------------------------
; Input : None
; Output : Bus communication, STOP condition
;-----------------------------------------------------------------------------
;
;Generate STOP bit (SDA goes from low to high during SCL high state)
;and check bus conditions.
BSTOP
bsf STATUS,RP0
bcf TRIS_C,SDA ; Return SDA to low
bsf TRIS_C,SCL ; Set SCL high
nop
movlw 1 ; Ready error code 1
bcf STATUS,RP0
btfss PORT_C,SCL ; High?
call ERR ; No, SCL locked low by device
bsf STATUS,RP0
bsf TRIS_C,SDA ; SDA goes from low to high during SCL
high
movlw 4 ; Ready error code 4
btfss TRIS_C,SDA ; High?
call ERR ; No, SDA bus not release for STOP
bcf STATUS,RP0
retlw 0
;
;-----------------------------------------------------------------------------
; Two wire/I2C - CPU communication error status table and subroutine
;-----------------------------------------------------------------------------
; input : W-reg = error code
; output : ERCODE = error code
; FLAG(ERROR) = 1
;
; code error status mode
; -------
------------------------------------------------------
; 1 : SCL locked low by device (bus is still busy)
; 2 : SDA locked low by device (bus is still busy)
; 3 : No acknowledge from device (no handshake)
; 4 : SDA bus not released for master to generate STOP
bit
;-----------------------------------------------------------------------------
;
;Subroutine to identify the status of the serial clock (SCL) and serial
data
;(SDA) condition according to the error status table. Codes generated are
;useful for bus/device diagnosis.
;
ERR
bcf STATUS,RP0
btfss FLAG,ERRORFLG ; If not first error, do not change code
movwf ERCODE ; Save error code
bsf FLAG,ERRORFLG ; Set error flag
retlw 0
END