I2C Bus interface

I2C Bus interface
Hardware

i2cbus

The connector on the top left of the diagram is from my own 6502 boards (see the sbc project) and is as it is for two reasons. It’s easy to wire on a stripboard layout and I have a lot of 26 way ribbon, headers and plugs. All the signals are directly from the 6502 except /SEL0 and /SEL1 which are used to select the block $F1xx with /SEL0 = 1 and /SEL1 = 0.

There is no socket shown for the I2C bus, this is up to the user.The two capacitors are low ESR electrolytics and are placed near the GAL and between the two chips. If you don’t have this type to hand you can use standard electrolytics with some low value ceramic capacitor, say 0.1uF, in parallel.

The GAL16V8A is used purely to generate the read and write strobes. Each is a negative going pulse coincident with phase 2. The interface uses just one byte in the address range. For anyone interested the equations for this chip are in i2c_01.pld and can be compiled with WinCUPL. The fuse file, i2c_01.jed and the compiler list file i2c_01.txt are also included.

The 74LS74 is used to latch the two lowest bits of the data bus during write access to the interface. The reset line is connected so that both of these outputs are set at startup (this disables the I2C bus until required). This is very similar to my AT keyboard with the exeption that reset sets the opposite state.
The outputs from the latches are used to drive the enable pins on two of the four buffers from the 74LS125, these are then used to drive the data and clock lines of the I2C bus. The buffers have their inputs tied low so behave like open collector outputs when used like this. The other two buffers are used to drive the data bus during read access.

The finished board

board plusteletext

256k byte memory

mem

Software

The software has a four main routines to handle the I2C bus

SendAddr Send start and slave address to the I2C bus.
SendData Send data byte(s) to an addressed device.
ReadData Read data byte(s) from an addressed device.
StopI2c generates a stop condition on the i2c bus.

This is a description of all the I2C routines

SendAddr
This routine sends the slave address to the I2C bus. There are a number of locations that need set-up before this routine is called. Each device has an 8 bit address, the lowest bit of which is a read/write bit, this address is set in I2cAddr. Next is the byte count, if you are just addressing the device this can be zero but otherwise it is the byte pair in I2cCountL/H. Lastly, if there is data to be sent, is the buffer pointer TxBuffL/H. This should be set to the start of the data to be sent. If all is well this routine exits with Cb=0 and the bus in an held state, you can then either send data, receive data or just send stop.

ReadData
This routine reads I2cCountL/H bytes from an already addressed device. It should be entered with RxBuffL/H pointing to a suitable buffer area. On exit Cb=0 if there were no errors and the I2C bus is in a held state, you can then either receive more data or just send stop.

SendData
The same as ReadData but sends I2cCountL/H bytes to an already addressed device. Again on exit Cb=0 if there were no errors and the I2C bus is in a held state, you can then either send more data or just send stop.

StopI2c
This routine just generates a stop condition on i2c bus. On entry it is assumed only that the clock is held low.

ByteIn
Read a byte from the I2C bus, the byte is returned in A. Entry to this routine should be with the bus in a held state and it exits with the bus in the same state. Note there is no timeout on this routine so it could end up waiting for ever. After this routine you should send an ack but if it’s the end of what you want you can just send stop.

ByteOut
Send a byte to the I2C bus, the byte to be sent is in A. Entry to this routine should be with the bus in a held state and it exits with the bus in the same state. Note there is no timeout on this routine so it could end up waiting for ever. Returns with the ack bit in Cb=0.

DoAck
Send ack bit, the ack bit state to send is in Cb. Entry is with the clock low, then ack needs to be set and then the clock released. The routine then waits for the clock to rise before pulling it low and then exiting.

GetAck
Get the ack bit, the received ack bit is returned in Cb. Entry is with the clock low, then the data line is released followed by the clock. Then, once the clock rises, the ack bit is read.

View the I2C driver assembler source

EHBASIC teletext driver. This is a simple page select driver for the SAA5243 + SAA5231 teletext chipset

The board in use and screen shots
inuse
nick

toon

ch5

cnn

dsny

mtv


I2C Driver ASM

;------------------------------------------------------------------------------------
;
; The following is 6502 code for an I2C driver. It acts only as master.
;
; I2C uses two bi-directional (OC) lines: clock and data. The maximum bit rate for
; slow mode is 100kbits/sec (fast mode is not supported) but with a 1.8MHz 6502 the
; best you will get is about 43kbits/sec. As the 6502, which is the master, controls
; the clock line, the processor speed should not be a problem.
;
; To work as a slave the 6502 would need extra hardware to detect the start condition,
; the stop condition and extra code to handle collisions.
; This is saved for a later project.
;
; Devices are accessed using the following four subroutines.
;
; SendAddr
;	This routine sends the slave address to the I2C bus. It can also send any
;	required register address bytes by setting them up as you would data to be sent.
;	No stop is sent so you can either read or write after calling this routine.
; SendData
;	Send data byte(s) to an addressed device. Set the count in I2cCountL/H and
;	point to the data with TxBuffL/H. No stop is sent after calling this routine.
; ReadData
;	Read data byte(s) from an addressed device. Set the count in I2cCountL/H and
;	point to the buffer with RxBuffL/H. No stop is sent after calling this routine.
; StopI2c
;	generates a stop condition on the i2c bus
;
; Each device has an 8 bit address, the lowest bit of which is a read/write bit.
;
;------------------------------------------------------------------------------------
I2CPort	=	$F121			; i2c bus port, o.c. outputs, tristate inputs
; bit 0 is data  [SDA]
; bit 1 is clock [SLC]
; bits 2 to 7 are unused
RxBuffL		=	$F1		; receive buffer pointer low byte
TxBuffL		=	RxBuffL		; the same (can't do both at once!)
RxBuffH		=	$F2		; receive buffer pointer high byte
TxBuffH		=	RxBuffH		; the same (can't do both at once!)
ByteBuff	=	$F3		; byte buffer for Tx/Rx routines
I2cAddr		=	$F4		; Tx/Rx address
I2cCountL	=	$F5		; Tx/Rx byte count low byte
I2cCountH	=	$F6		; Tx/Rx byte count high byte
;------------------------------------------------------------------------------------
*=	$2000
JMP	SendData		; vector to send data
JMP	ReadData		; vector to read data
JMP	SendAddr		; vector to send slave address
JMP	StopI2c			; vector to send stop
;------------------------------------------------------------------------------------
;
; send the slave address for an i2c device. if I2cCountL is non zero then that number
; of bytes will be sent after the address (to allow register addressing, required on
; some devices). RxBuff is a pointer, in page zero, to the transmit buffer exits with
; the clock low and Cb=0 if all ok routine entered with the i2c bus in a stopped state
; [SDA=SCL=1]
SendAddr
LDA	I2CPort			; get i2c port state
ORA	#$01			; release data
STA	I2CPort			; out to i2c port
LDA	#$03			; release clock
STA	I2CPort			; out to i2c port
LDA	#$01			; set for data test
WaitAD
BIT	I2CPort			; test the clock line
BEQ	WaitAD			; wait for the data to rise
LDA	#$02			; set for clock test
WaitAC
BIT	I2CPort			; test the clock line
BEQ	WaitAC			; wait for the clock to rise
JSR	StartI2c		; generate start condition
LDA	I2cAddr			; get address (including read/write bit)
JSR	ByteOut			; send address byte
BCS	StopI2c			; branch if no ack
LDA	I2cCountL		; get byte count
BNE	SendData		; go send if not zero
RTS				; else exit
;------------------------------------------------------------------------------------
;
; send data to an already addressed i2c device. I2cCountL/H is the number of bytes to
; send RxBuff is a pointer, in page zero, to the transmit buffer exits with Cb=0 if
; all ok. it is assumed at least one byte is to be sent routine entered with the i2c
; bus in a held state [SCL=0]
SendData
INC	I2cCountH		; increment count high byte
LDY	#$00			; set index to zero
WriteLoop
LDA	(RxBuffL),Y		; get byte from buffer
JSR	ByteOut			; send byte to device
BCS	StopI2c			; branch if no ack
INY				; increment index
BNE	NoHiWrInc		; branch if no rollover
INC	RxBuffH			; else increment pointer high byte
NoHiWrInc
DEC	I2cCountL		; decrement count low byte
BNE	WriteLoop		; loop if not all done
DEC	I2cCountH		; increment count high byte
BNE	WriteLoop		; loop if not all done
RET
;------------------------------------------------------------------------------------
;
; get data from already addressed i2c device. I2cCountL/H is the number of bytes to
; get, RxBuff is a pointer, in page zero, to the receive buffer. exits with Cb = 0 if
; all ok it is assumed at least one byte is to be received. the routine is entered
; with the i2c bus in a held state [SCL=0]
ReadData
LDY	#$00			; set index to zero
ReadLoop
DEC	I2cCountL		; decrement count low byte
JSR	ByteIn			; get byte from device
LDA	I2cCountL		; get count low byte
CMP	#$01			; compare with end count + 1
LDA	I2cCountH		; get count high byte
SBC	#$00			; subtract carry, leaves Cb = 0 for last byte
JSR	DoAck			; send ack bit
LDA	ByteBuff		; get byte from byte buffer
STA	(TxBuffL),Y		; save in device buffer
INY				; increment index
BNE	NoHiRdInc		; branch if no rollover
INC	TxBuffH			; else increment pointer high byte
NoHiRdInc
LDA	I2cCountL		; get count low byte
BNE	ReadLoop		; loop if not all done
DEC	I2cCountH		; decrement count high byte
LDA	I2cCountH		; get count high byte
CMP	#$FF			; compare with end count
BNE	ReadLoop		; loop if not all done
RTS
;------------------------------------------------------------------------------------
;
; generate stop condition on i2c bus. it is assumed only that the clock is low on
; entry to this routine.
StopI2c
LDA	#$00			; now hold the data down
STA	I2CPort			; out to i2c port
;	NOP				; need this if running > 1.9MHz
LDA	#$02			; release the clock
STA	I2CPort			; out to i2c port
;	NOP				; need this if running > 1.9MHz
LDA	#$03			; now release the data (stop)
STA	I2CPort			; out to i2c port
RTS
;------------------------------------------------------------------------------------
;
; generate start condition on i2c bus. it is assumed that both clock and data are
; high on entry to this routine. note, another condition is A = $02 on entry
StartI2c
STA	I2CPort			; out to i2c port
;	NOP				; need this if running > 1.9MHz
LDA	#$00			; clock low, data low
STA	I2CPort			; out to i2c port
RTS
;------------------------------------------------------------------------------------
;
; output byte to 12c bus, byte is in A. returns Cb = 0 if ok. clock should be low
; after generating a start or a previously sent byte
; exits with clock held low
ByteOut
STA	ByteBuff		; save byte for transmit
LDX	#$08			; 8 bits to do
OutLoop
LDA	#$00			; unshifted clock low
ROL	ByteBuff		; bit into carry
ROL	A			; get data from carry
STA	I2CPort			; out to i2c port
;	NOP				; need this if running > 1.9MHz
ORA	#$02			; clock line high
STA	I2CPort			; out to i2c port
LDA	#$02			; set for clock test
WaitT1
BIT	I2CPort			; test the clock line
BEQ	WaitT1			; wait for the clock to rise
LDA	I2CPort			; get data bit
AND	#$01			; set clock low
STA	I2CPort			; out to i2c port
DEX				; decrement count
BNE	OutLoop			; branch if not all done
;------------------------------------------------------------------------------------
;
; clock is low, data needs to be released, then the clock needs to be released then
; we need to wait for the clock to rise and get the ack bit.
GetAck
LDA	#$01			; float data
STA	I2CPort			; out to i2c port
LDA	#$03			; float clock, float data
STA	I2CPort			; out to i2c port
LDA	#$02			; set for clock test
WaitGA
BIT	I2CPort			; test the clock line
BEQ	WaitGA			; wait for the clock to rise
LDA	I2CPort			; get data
LSR	A			; data bit to Cb
LDA	#$01			; clock low, data released
STA	I2CPort			; out to i2c port
RTS
;------------------------------------------------------------------------------------
;
; input byte from 12c bus, byte is returned in A. entry should be with the clock low
; after generating a start or a previously sent byte
; exits with clock held low
ByteIn
LDX	#$08			; 8 bits to do
LDA	#$01			; release data
STA	I2CPort			; out to i2c port
InLoop
LDA	#$03			; release clock
STA	I2CPort			; out to i2c port
LDA	#$02			; set for clock test
WaitR1
BIT	I2CPort			; test the clock line
BEQ	WaitR1			; wait for the clock to rise
LDA	I2CPort			; get data
ROR	A			; bit into carry
ROL	ByteBuff		; bit into buffer
LDA	#$01			; set clock low
STA	I2CPort			; out to i2c port
DEX				; decrement count
BNE	InLoop			; branch if not all done
RTS
;------------------------------------------------------------------------------------
;
; clock is low, ack needs to be set then the clock released then we wait for the
; clock to rise before pulling it low and finishing. Ack bit is in Cb
DoAck
LDA	#$00			; unshifted clock low
ROL	A			; get ack from carry
STA	I2CPort			; out to i2c port
;	NOP				; need this if running > 1.9MHz
ORA	#$02			; release clock
STA	I2CPort			; out to i2c port
LDA	#$02			; set for clock test
WaitTA
BIT	I2CPort			; test the clock line
BEQ	WaitTA			; wait for the clock to rise
LDA	I2CPort			; get ack back
AND	#$01			; hold clock
STA	I2CPort			; out to i2c port
RTS
;------------------------------------------------------------------------------------
END


EhBASIC Teletext page viewer
This is a simple page select driver for the SAA5243 + SAA5231 teletext chipset. X is valid as a wildcard digit.

1 REM set memory size to 8192 for this program
5 REM simple teletext decoder page driver
6 REM there is no page read, output is via
7 REM teletext chip video out
10 REM set I2C interface values
20 TT = 34 : REM teletext chip 12c address
30 SB = $2000 : REM send byte
40 RB = £2003 : REM read byte (not used)
50 CL = $F5 : REM # bytes low (i2ccountL)
60 BL = $F1 : REM buffer ptr low  (rxbuffl)
70 AD = $F4 : REM device address (i2caddr)
80 BF = $4000 : REM buffer address
90 DIM TR(10) : REM register buffer
110 GOSUB 800 : REM setup chip
120 TR(8) = 0 : REM no clear display
130 TR(9) = 0 : REM set row
140 TR(10) = 0 : REM set column
150 GOSUB 838 : REM set registers 8 to 10
160 P3 = 49 : REM 1
161 P2 = 48 : REM 0
162 P1 = 48 : REM 0
170 GOSUB 370 : REM set search page
200 REM main program loop
210 DO
220 GOSUB 300 : REM select page
230 LOOP
299 END : REM never gets here
300 REM Select page
310 INPUT "Page no.";P$
320 IF LEN(P$)<>3 THEN 310
330 P$ = UCASE$(P$) : REM "x" to "X"
340 P1=ASC(RIGHT$(P$,1)) : REM 1s character ASCII value
350 P2=ASC(MID$(P$,2,1)) : REM 10s character ASCII value
360 P3=ASC(LEFT$(P$,1)) : REM 100s character ASCII value
365 REM dispaly the searched for page number
370 POKE BF,8 : REM register address
380 POKE BF+1,0 : REM set x value
390 POKE BF+3,0 : REM set y value
400 POKE BF+3,2 : REM set white
410 POKE BF+4,P3 : REM display page 100s
420 POKE BF+5,P2 : REM display page 10s
430 POKE BF+6,P1 : REM display page 1s
440 POKE AD,TT : REM set device address
450 DOKE BL,BF : REM set the buffer address
460 DOKE CL,7 : REM seven bytes to send
470 CALL SB : REM send byte(s)
475 REM set the page to search for
480 P1=P1-32 : REM calsulate page 1s (ASCII - 48 + 16)
490 P2=P2-32 : REM calculate page 10s (ASCII - 48 + 16)
500 P3=P3-24 : REM calculate page 100s (ASCII - 48 + 24)	
510 IF P1=56 THEN P1 = 0 : REM allow wildcard "X"
520 IF P2=56 THEN P2 = 0 : REM allow wildcard "X"
530 IF P3=64 THEN P3 = 8 : REM allow wildcard "X"
540 POKE BF,2 : REM register address
550 POKE BF+1,0
560 POKE BF+2,P3
570 POKE BF+3,P2
580 POKE BF+4,P1
590 POKE AD,TT : REM set device address
600 DOKE BL,BF : REM set the buffer address
610 DOKE CL,5 : REM five bytes to send
620 CALL SB : REM send byte(s)
630 RETURN
799 END
800 REM setup teletext registers
801 RESTORE 910
802 FOR X = 1 TO 5
804 READ TR(X)
806 POKE BF+X,TR(X)
808 NEXT
810 POKE BF,1 : REM register address
812 POKE AD,TT : REM set device address
814 DOKE BL,BF : REM set the buffer address
816 DOKE CL,6 : REM six bytes to send
818 CALL SB : REM send byte
819 RESTORE 935
820 FOR X = 4 TO 7
822 READ TR(X)
824 POKE BF-3+X,TR(X)
826 NEXT
828 POKE BF,4 : REM register address
830 POKE AD,TT : REM set device address
832 DOKE BL,BF : REM set the buffer address
834 DOKE CL,5 : REM five bytes to send
836 CALL SB : REM send byte
838 RESTORE 980
839 FOR X = 8 TO 10
840 READ TR(X)
842 POKE BF-7+X,TR(X)
844 NEXT
846 POKE BF,8 : REM register address
848 POKE AD,TT : REM set device address
850 DOKE BL,BF : REM set the buffer address
852 DOKE CL,4 : REM four bytes to send
854 CALL SB : REM send byte
856 RETURN
900 REM default values for registers 1 - 3 
910 DATA 4 
920 DATA 0
930 DATA 25,16,16
935 REM default values for registers 4 - 7
940 DATA 0
950 DATA 207
960 DATA 0
970 DATA 39
975 REM default values for registers 8 - 10
980 DATA 16
985 DATA 0
990 DATA 0
[code]
<a name="i2c_jed"></a>
<b>GAL logic fuse file</B>
[code]
CUPL(WM)        4.7b  Serial# XX-xxxxxxxx
Device          g16v8as  Library DLIB-h-36-2	
Created         Fri Mar 23 10:30:16 2001
Name            I2C_01 
Partno          00 
Revision        01 
Date            19/03/01 
Designer        Lee 
Company         
Assembly        None 
Location        
*QP20 
*QF2194 
*G0 
*F0 
*L00000 10101011011110110111011010010110
*L00256 10101011011110110111101010010110
*L02048 00000000001100000011000000100000
*L02112 00000000001111111111111111111111
*L02144 11111111111111111111111111111111
*L02176 111111111111111110
*C0E15
*77C0


GAL PLD

Name     I2C_01 ;
PartNo   00 ;
Date     19/03/01 ;
Revision 01 ;
Designer Lee ;
Company   ;
Assembly None ;
Location  ;
Device   g16v8as ;
/* This GAL is the select logic for the I2C interface board	*/
/* Logic minimisations		None				*/
/* Optimisations			None				*/
/* Download				JEDEC/POF/PRG		*/
/* Doc File Options		fuse plot, equations	*/
/* Output				None				*/
/* *************** INPUT PINS *********************/
PIN	1 = A4	;				/* address bus		*/ 
PIN	2 = A3	;				/* address bus		*/ 
PIN	3 = A2	;				/* address bus		*/ 
PIN	4 = A0	;				/* address bus		*/ 
PIN	5 = A1	;				/* address bus		*/ 
PIN	6 = p02	;				/* CPU phase 2		*/ 
PIN	7 = RW	;				/* read write		*/ 
PIN	8 = !SEL1	;				/* block select		*/ 
PIN	9 = !SEL0	;				/* block select		*/ 
PIN	11 = A6	;				/* address bus		*/ 
PIN	12 = A5	;				/* address bus		*/ 
PIN	13 = A7	;				/* address bus		*/ 
/* *************** OUTPUT PINS *********************/
PIN  19 = !I2CR		;			/* I2C port read strobe		*/ 
PIN  18 = !I2CW		;			/* I2C port write strobe	*/ 
/*PIN  17 = 		;			/* 					*/ 
/*PIN  16 = 		;			/* 					*/ 
/*PIN  15 = 		;			/* 					*/ 
/*PIN  14 = 		;			/* 					*/ 
/* intermediate terms */
ADDR		= !A7 & !A6 & A5 & !A4 & !A3 & !A2 & !A1 & A0 & !SEL0 & SEL1 ;
/* F121h (0010 0001)
/* Output terms */
I2CR	= ADDR &  RW & p02 ;			/* I2C port read strobe		*/
I2CW	= ADDR & !RW & p02 ;			/* I2C port write strobe	*/



*******************************************************************************
I2C_01
*******************************************************************************
CUPL(WM)        4.7b Serial# XX-xxxxxxxx
Device          g16v8as  Library DLIB-h-36-2
Created         Fri Mar 23 10:30:16 2001
Name            I2C_01 
Partno          00 
Revision        01 
Date            19/03/01 
Designer        Lee 
Company
Assembly        None 
Location        
===============================================================================
Expanded Product Terms
===============================================================================
ADDR =>
A0 & !A1 & !A2 & !A3 & !A4 & A5 & !A6 & !A7 & !SEL0 & SEL1
KBR =>
A0 & !A1 & !A2 & !A3 & !A4 & A5 & !A6 & !A7 & RW & !SEL0 & SEL1 & p02
KBW =>
A0 & !A1 & !A2 & !A3 & !A4 & A5 & !A6 & !A7 & !RW & !SEL0 & SEL1 & p02
===============================================================================
Symbol Table
===============================================================================
Pin Variable                                    Pterms   Max     Min    
Pol   Name              Ext     Pin     Type     Used   Pterms  Level   
--- --------            ---     ---     ----    ------  ------  -----   
A0                          4        V        -       -       -     
A1                          5        V        -       -       -     
A2                          3        V        -       -       -     
A3                          2        V        -       -       -     
A4                          1        V        -       -       -     
A5                          12       V        -       -       -     
A6                          11       V        -       -       -     
A7                          13       V        -       -       -     
ADDR                        0        I        1       -       -     
!  KBR                         19       V        1       8       1     
!  KBW                         18       V        1       8       1     
RW                          7        V        -       -       -     
!  SEL0                        9        V        -       -       -     
!  SEL1                        8        V        -       -       -     
p02                         6        V        -       -       -     
LEGEND    D : default variable         F : field      G : group
I : intermediate variable    N : node       M : extended node
U : undefined                V : variable   X : extended variable
T : function
===============================================================================
Fuse Plot
===============================================================================
Syn   02192 - Ac0   02193 x 
Pin #19  02048  Pol x  02120  Ac1 x 
00000 -x-x-x--x----x--x---x--x-xx-x--x 
00032 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
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00128 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
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Pin #18  02049  Pol x  02121  Ac1 x 
00256 -x-x-x--x----x--x----x-x-xx-x--x 
00288 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
00320 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
00352 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
00384 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
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Pin #17  02050  Pol x  02122  Ac1 - 
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Pin #16  02051  Pol x  02123  Ac1 - 
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Pin #15  02052  Pol x  02124  Ac1 - 
01024 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
01056 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
01088 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
01120 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
01152 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
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Pin #14  02053  Pol x  02125  Ac1 - 
01280 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
01312 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
01344 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
01376 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
01408 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
01440 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
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Pin #13  02054  Pol x  02126  Ac1 - 
01536 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
01568 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
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01728 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
01760 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
Pin #12  02055  Pol x  02127  Ac1 - 
01792 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
01824 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
01856 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
01888 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
01920 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
01952 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
01984 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
02016 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
LEGEND    X : fuse not blown 
- : fuse blown 
===============================================================================
Chip Diagram
===============================================================================
______________
|    I2C_01    |
A4 x---|1           20|---x Vcc                      
A3 x---|2           19|---x !KBR                     
A2 x---|3           18|---x !KBW                     
A0 x---|4           17|---x                          
A1 x---|5           16|---x                          
p02 x---|6           15|---x                          
RW x---|7           14|---x                          
!SEL1 x---|8           13|---x A7                       
!SEL0 x---|9           12|---x A5                       
GND x---|10          11|---x A6                       
|______________|