Datasheet

Data Sheet ADM1178
Rev. D | Page 17 of 24
WRITE AND READ OPERATIONS
The I
2
C specification defines several protocols for different types of
read and write operations. The operations used in the ADM1178
are discussed in this section. Table 6 shows the abbreviations
used in the command diagrams (see Figure 38 to Figure 43).
Table 6. I
2
C Abbreviations
Abbreviation Condition
S Start
P Stop
R Read
W Write
A
Acknowledge
N No acknowledge
QUICK COMMAND
The quick command operation allows the master to check if the
slave is present on the bus, as follows:
1. The master device asserts a start condition on SDA.
2. The master sends the 7-bit slave address, followed by the
write bit (low).
3. The addressed slave device asserts an acknowledge on SDA.
4. The master asserts a stop condition on SDA to end the
transaction.
06048-009
S
SLAVE
ADDRESS
W A
1 2 3
P
4
Figure 38. Quick Command
WRITE COMMAND BYTE
In the write command byte operation, the master device sends
a command byte to the slave device, as follows:
1. The master device asserts a start condition on SDA.
2. The master sends the 7-bit slave address, followed by the
write bit (low).
3. The addressed slave device asserts an acknowledge on SDA.
4. The master sends the command byte. The command byte is
identified by an MSB = 0. An MSB = 1 indicates an extended
register write (see the Write Extended Command Byte
section).
5. The slave asserts an acknowledge on SDA.
6. The master asserts a stop condition on SDA to end the
transaction.
S
SLAVE
ADDRESS
W A
COMMAND
BYTE
A P
1 2 3 4 5 6
06048-010
Figure 39. Write Command Byte
The seven LSBs of the command byte are used to configure and
control the ADM1178. Table 7 provides details of the function
of each bit.
Table 7. Command Byte Operations
Bit Default Name Function
C0 0 V_CONT
LSB, set to convert voltage continuously. If readback is attempted before the first conversion is complete,
the ADM1178 asserts an acknowledge and returns all 0s in the returned data.
C1 0 V_ONCE Set to convert voltage once. Self-clears. I
2
C asserts a no acknowledge on attempted reads until the ADC
conversion is complete.
C2
0
I_CONT
Set to convert current continuously. If readback is attempted before the first conversion is complete, the
ADM1178 asserts an acknowledge and returns all 0s in the returned data.
C3 0 I_ONCE Set to convert current once. Self-clears. I
2
C asserts a no acknowledge on attempted reads until the ADC
conversion is complete.
C4 0 VRANGE Selects different internal attenuation resistor networks for voltage readback. A 0 in C4 selects a 14:1
voltage divider. A 1 in C4 selects a 7:2 voltage divider. With an ADC full scale of 1.902 V, the voltage at the
VCC pin for an ADC full-scale result is 26.35 V for VRANGE = 0 and 6.65 V for VRANGE = 1.
C5 0 Not applicable Unused.
C6 0 STATUS_RD Status read. When this bit is set, the data byte read back from the ADM1178 is the status byte. This
contains the status of the device alerts. See Table 15 for full details of the status byte.