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Two-Wire Serial Communication
Interface Description
The DS90C3202 operates as a slave on the Serial Bus, so
the S2CLK line is an input (no clock is generated by the
DS90C3202) and the S2DAT line is bi-directional.
DS90C3202 has a fixed 7bit slave address. The address is
not user configurable in anyway.
A zero in front of the register address is required. For ex-
ample, to access register 0x0Fh, “0F” is the correct way of
accessing the register.
COMMUNICATING WITH THE DS90C3202 CONTROL
REGISTERS
There are 32 data registers (one byte each) in the
DS90C3202, and can be accessed through 32 addresses.
All registers are predefined as read only or read and write.
The DS90C3202 slave state machine does not require an
internal clock and it supports only byte read and write. Page
mode is not supported. The 7bit binary address is 0111110
All seven bits are hardwired internally.
Readingthe DS90C3202can takeplaceeither ofthree ways:
1. If the location latched in the data register addresses is
correct, then the read can simply consist of a slave
address byte, followed by retrieving the data byte.
2. If the data register address needs to be set, then a slave
address byte, data register address will be sent first,
then the master will repeat start, send the slave address
byte and data byte to accomplish a read.
3. When performing continuous read operations, another
write (or read) instruction in between reads needs to be
completed in order for the two-wire serial interface mod-
ule to read repeatedly.
The data byte has the most significant bit first. At the end of
a read, the DS90C3202 can accept either Acknowledge or
No Acknowledge from the Master (No Acknowledge is typi-
cally used as a signal for the slave that the Master has read
its last byte).
The master must generate a Start by sending the 7-bit slave
address plus a 0 first, and wait for acknowledge from
DS90C3202. When DS90C3202 acknowledges (the 1st
ACK) that the master is calling, the master then sends the
data register address byte and waits for acknowledge from
the slave. When the slave acknowledges (the 2nd ACK), the
master repeats the “Start” by sending the 7-bit slave address
plus a 1 (indicating that READ operation is in progress) and
waits for acknowledge from DS90C3202. After the slave
responds (the 3rd ACK), the slave sends the data to the bus
and waits for acknowledge from the master. When the mas-
ter acknowledges (the 4th ACK), it generates a “Stop”. This
completes the “ READ”.
A Write to the DS90C3202 will always include the slave
address, data register address byte, and a data byte.
The master must generate a “Start” by sending the 7-bit
slave address plus a 0 and wait for acknowledge from
DS90C3202. When DS90C3202 acknowledges (the 1st
ACK) that the master is calling, the master then sends the
data register address byte and waits for acknowledge from
the slave. When the slave acknowledges (the 2nd ACK), the
master sends the data byte and wait for acknowledge from
the slave. When the slave acknowledges (the 3rd ACK), the
master generates a “ Stop”. This completes the “WRITE”.
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FIGURE 17. Byte Read
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FIGURE 18. Byte Write
DS90C3202
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