Datasheet

Data Sheet ADM1178
Rev. D | Page 19 of 24
READ VOLTAGE AND/OR CURRENT DATA BYTES
Depending on how the device is configured, ADM1178 can be
set up to provide information in three ways after a conversion
(or conversions): voltage and current readback, voltage only
readback, and current only read back. See the Write Command
Byte section for more details.
Voltage and Current Readback
The ADM1178 digitizes both voltage and current. Three bytes
are read back in the format shown in Table 12.
Table 12. Voltage and Current Readback Format
Byte Contents B7 B6 B5 B4 B3 B2 B1 B0
1 Voltage MSBs V11 V10 V9 V8 V7 V6 V5 V4
2 Voltage MSBs I11 I10 I9 I8 I7 I6 I5 I4
3 Voltage LSBs V3 V2 V1 V0 I3 I2 I1 I0
Voltage Readback
The ADM1178 digitizes voltage only. Two bytes are read back in
the format shown in Table 13.
Table 13. Voltage Only Readback Format
Byte Contents B7 B6 B5 B4 B3 B2 B1 B0
1 Voltage MSBs V11 V10 V9 V8 V7 V6 V5 V4
2 Voltage LSBs V3 V2 V1 V0 0 0 0 0
Current Readback
The ADM1178 digitizes current only. Two bytes are read back
in the format shown in Table 14.
Table 14. Current Only Readback Format
Byte Contents B7 B6 B5 B4 B3 B2 B1 B0
1 Current MSBs I11 I10 I9 I8 I7 I6 I5 I4
2 Current LSBs I3 I2 I1 I0 0 0 0 0
The following series of events occurs when the master receives
three bytes (voltage and current data) from the slave device:
1. The master device asserts a start condition on SDA.
2. The master sends the 7-bit slave address, followed by the
read bit (high).
3. The addressed slave device asserts an acknowledge on SDA.
4. The master receives the first data byte.
5. The master asserts an acknowledge on SDA.
6. The master receives the second data byte.
7. The master asserts an acknowledge on SDA.
8. The master receives the third data byte.
9. The master asserts a no acknowledge on SDA.
10. The master asserts a stop condition on SDA, and the
transaction ends.
For cases where the master is reading voltage only or current
only, two data bytes are read and Step 7 and Step 8 are not required.
S
SLAVE
ADDRESS
R A
DATA 1 DATA 2
N PDATA 3A
A
1 2 3 4 5 6 7 8 9 10
06048-012
Figure 41. Three-Byte Read from ADM1178
06048-013
S
SLAVE
ADDRESS
R A
DATA 1
N PDATA 2
A
1 2 3 4 5 6 7 8
Figure 42. Two-Byte Read from ADM1178
Converting ADC Codes to Voltage and Current Readings
Equation 10 and Equation 11 can be used to convert ADC codes
representing voltage and current from the ADM1178 12-bit
ADC into actual voltage and current values.
Voltage = (V
FULLSCALE
/4096) × Code (10)
where:
V
FULLSCALE
= 6.65 V (7:2 range) or 26.35 V (14:1 range).
Code is the ADC voltage code read from the device
(Bit V11 to Bit V0).
Current = ((I
FULLSCALE
/4096) × Code)/Sense Resistor (11)
where:
I
FULLSCALE
= 105.84 mV.
Code is the ADC current code read from the device
(Bit I11 to Bit I0).
Read Status Register
A single register of status data can also be read from the
ADM1178 as follows:
1. The master device asserts a start condition on SDA.
2. The master sends the 7-bit slave address, followed by the
read bit (high).
3. The addressed slave device asserts an acknowledge on SDA.
4. The master receives the status byte.
5. The master asserts an acknowledge on SDA.
06048-014
S
SLAVE
ADDRESS
STATUS
BYTE
R A
A
1 2 3 4 5
Figure 43. Status Read from ADM1178
Table 15 shows the ADM1178 STATUS registers in detail. Note
that Bit 1, Bit 3, and Bit 5 are cleared by writing to Bit 4 (the
CLEAR bit) of the ALERT_EN register.