Modified 24LC128 example code to write 12 bits but it doesn't work???

wmtell1

I modified the example code for the 24LC128 to write a 16 bit word and it correctly wrote the 16 bits. Since I'm now using a 12 bit LT1298 I don't need to write 16 bits and·I've modified the code to write 12 bits. The program·displays·the value of NIB2 using the DEBUG window and it shows the correct value but a [noparse][[/noparse]0] is incorrectly written. Does anyone have a clue as to what's happening?


' {$STAMP BS2sx}
' {$PBASIC 2.5}
' {$PORT COM5}
' Purpose...Write a 12 bit word to a 24LC128 EEPROM
'
' =========================================================================
'
'

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' Program Description
'

---

'
'WRITE a 12 bit word via a subroutine to a 24LC128 EEPROM address,
'starting at 1, incrementing by 2 and ending at address 4095.
'Flash an LED ON/OFF to confirm each WRITE cycle.
'
'

---

'
'

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[noparse][[/noparse] I/O Definitions ]

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LED PIN 4
SDA PIN 5 ' I2C Serial Data Line
SCL PIN 6 ' I2C Serial Clock Line
'

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[noparse][[/noparse] Constants ]

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Address CON $A0 ' Address Of 24LC128
Ack CON 0 ' Acknowledge Bit
'

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[noparse][[/noparse] Variables ]

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temp VAR Word ' Variable Used For Work
i2cWork VAR Word ' Work Byte For I2C I/O
i2cWork1 VAR Word ' Work Byte For I2C I/O
i2cWork2 VAR Word ' Work Byte For I2C I/O
i2cAck VAR Bit ' Ack Bit From Device
eeprom_add VAR Word ' EEPROM Address
J···· VAR········ Nib
'

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[noparse][[/noparse] Main Routine ]

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FOR temp = 1 TO 4095 STEP 2
· eeprom_add = temp
· GOSUB WriteEE
NEXT 'temp
END
'

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[noparse][[/noparse] Subroutines ]

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· ' Writing Section
WriteEE:
FOR J = 1 TO 2
· GOSUB I2C_Start
· GOSUB Control_Byte_Write
· GOSUB Addrs
· GOSUB I2C_Write
· GOSUB I2C_Stop
· PAUSE 100
NEXT 'J
RETURN
I2C_Stop: ' I2C Stop Bit Sequence
LOW SDA
INPUT SCL
INPUT SDA ' SDA --> High While SCL High
RETURN
I2C_Start: ' I2C Start Bit Sequence
INPUT SDA
INPUT SCL
LOW SDA ' SDA --> Low While SCL High
RETURN
Control_Byte_Write: ' I2C Control Write Byte Sequence
i2cWork = Address
i2cWork.BIT0 = 0 ' Sets Unit To Write
SHIFTOUT SDA, SCL, MSBFIRST, [noparse][[/noparse]i2cWork\8] ' Send Byte To Device
SHIFTIN SDA, SCL, MSBPRE, [noparse][[/noparse]i2cAck\1] ' Get Acknowledge Bit
RETURN
Addrs: ' I2C Address Byte Sequence
i2cWork = eeprom_add· + J - 1
SHIFTOUT SDA, SCL, MSBFIRST, [noparse][[/noparse]i2cWork.HIGHBYTE\8] ' Send Byte To Device
SHIFTIN SDA, SCL, MSBPRE, [noparse][[/noparse]i2cAck\1] ' Get Acknowledge Bit
SHIFTOUT SDA, SCL, MSBFIRST, [noparse][[/noparse]i2cWork.LOWBYTE\8] ' Send Byte To Device
SHIFTIN SDA, SCL, MSBPRE, [noparse][[/noparse]i2cAck\1] ' Get Acknowledge Bit
RETURN
I2C_Write: ' I2C Write 2 Byte Sequence
IF J =1 THEN
· i2cWork = temp.LOWBYTE
· HIGH LED
SHIFTOUT SDA, SCL, MSBFIRST, [noparse][[/noparse]i2cWork\8] 'Send 8 bits (1 byte) To Device
ELSE
· i2cWork = temp.NIB2
· LOW LED
DEBUG "temp.NIB2= ",temp.NIB2,CR
SHIFTOUT SDA, SCL, MSBFIRST, [noparse][[/noparse]i2cWork\4] 'Send 4 bits To Device
ENDIF
SHIFTIN SDA, SCL, MSBPRE, [noparse][[/noparse]i2cAck\1] ' Get Acknowledge Bit
RETURN
Control_Byte_Read: ' I2C Control Read Byte Sequence
i2cWork = Address
i2cWork.BIT0 = 1 ' Sets Device To Read
SHIFTOUT SDA, SCL, MSBFIRST, [noparse][[/noparse]i2cWork\8] ' Send Byte To Device
SHIFTIN SDA, SCL, MSBPRE, [noparse][[/noparse]i2cAck\1] ' Get Acknowledge Bit
RETURN

Mike Green

You need to write 16 bits because that's how the 24LC128 is defined. By only writing 12 bits, you're relying on "accidental behavior" of the particular 24LC128 that you're using. Some 24LC128s may not write the 2nd byte at all. Others may be using the previous content of that memory location for the missing bit. Who knows? It depends on how the particular manufacturer has implemented the control logic (and they don't tell you that).