AL103 Revision 1.0
If the reset pin is held low, the AL103’s EEPROM interface will go into a high impedance state.
This feature is very useful for reprogramming the EEPROM during installation or reconfiguration.
The EEPROM can be reprogrammed by an external parallel port. For reprogramming using a
parallel port, a signal is used to hold the RESET pin low. The EEPROM interface will then be in the
high-impedance state. An external device can then program the EEPROM through the EEDIO and
the EECLK pins. The EEPROM address should be set to 000.
3.14.2 Start and Stop Bit
The write cycle is started by a start bit and ended by a stop bit. A start bit is a transition from high to
low of EEDIO when EEC is high. The operation terminates when EEDIO goes from low to high
when EEC is high. Following a start condition, the writing device must output the address of the
EEPROM. The most significant four bit of the EEPROM address is the device type identifier which
has an address of 1010. The EEPROM device address should be set to 000.
EECLK
EEDIO
Data or
Address
Valid
START
BIT
Data
Change
STOP BIT
Figure 5
EEPROM Start and Stop Bit
3.14.3 Write Cycle Operation
The EECLK is an output from the AL103 while EEDIO is a bi-directional signal. When accessing
the EEPROM, the reset pin has to be held low or initialization of the AL103 must be finished before
a writing operation can begin. A typical write operation is shown in Figure 6.
Device
Address
Start
Stop
A
A
A
S
S
8-Bit Data n
8-Bit Word Address
Acknowledge
Acknowledge
Acknowledge
Figure 6
EEPROM Write Cycle
9/00
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