Rainbow Electronics DS1846 - Manual (Page 4)

DS1846
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MEMORY ORGANIZATION
The DS1846’s serial EEPROM is internally organized with 32 pages. Each page contains 8 bytes. Each
byte requires an 8-bit address for random byte addressing. The address bytes, starting at F8h, contain the
wiper setting for the three potentiometers. The byte at address F8h determines the wiper setting for
potentiometer 1, which contains 256 positions. The byte at address F9h determines the wiper setting for
potentiometer 0, which contains 100 positions (00h to 63h). The byte at address FAh determines the
wiper setting for potentiometer 2, which contains 100 positions (00h to 63h). If a value greater than 63h
is written to either address F9h or FAh, the wiper is set according to the value in the seven least
significant bits and the MSB is ignored. Address locations FBh though FFh are reserved and should not
be written.
DEVICE OPERATION
Clock and Data Transitions: The SDA pin is normally pulled high with an external resistor or device.
Data on the SDA pin may only change during SCL low time periods. Data changes during SCL high
periods will indicate a start or stop conditions depending on the conditions discussed below. Refer to the
timing diagram Fig 2 for further details.
Start Condition: A high-to-low transition of SDA with SCL high is a start condition which must
precede any other command. Refer to the timing diagram Fig 2 for further details.
Stop Condition: A low-to-high transition of SDA with SCL high is a stop condition. After a read
sequence, the stop command places the DS1846 into a low-power mode. Refer to the timing diagram
Figure 2 for further details.
Acknowledge: All address and data bytes are transmitted via a serial protocol. The DS1846 pulls the
SDA line low during the ninth clock pulse to acknowledge that it has received each word.
Standby Mode: The DS1846 features a low-power mode that is automatically enabled after power-on,
after a stop command, and after the completion of all internal operations.
Memory Reset: After any interruption in protocol, power loss, or system reset, the following steps reset
the DS1846.
1. Clock up to nine cycles.
2. Look for SDA high in each cycle while SCL is high.
3. Create a start condition while SDA is high.
Device Addressing: The DS1846 must receive an 8-bit device address word following a start condition
to enable a specific device for a read or write operation. The address word is clocked into the DS1846
MSB to LSB. The address word consists of 101000 binary followed by A0 then the R/W
(READ/WRITE) bit. If the R/W bit is high, a read operation is initiated. The R/W is low, a write
operation is initiated. For a device to become active, the value of A0 must be the same as the hard-wired
address pins on the DS1846. Upon a match of written and hard-wired addresses, the DS1846 will output
a zero for one clock cycle as an acknowledge. If the address does not match the DS1846 returns to a
low-power mode.