ADM1178

Preliminary Technical Data

Rev. PrD | Page 10 of 16

VOLTAGE AND CURRENT READBACK

In addition to providing hot swap functionality, the ADM1178

also contains the components to allow voltage and current

sense amplifier and the voltage on the VCC pin are fed into a

12-bit ADC via a multiplexer. The device can be instructed to

convert voltage and/or current at any time during operation via

voltage and/or current values can be read out to 12-bit accuracy

in two or three bytes.

SERIAL BUS INTERFACE

Control of the ADM1178 is carried out via the Inter-IC Bus

max). The ADM1178 is connected to this bus as a slave device,

under the control of a master device.

The ADM1178 has a 7-bit serial bus slave address. When the

device is powered up, it will do so with a default serial bus

address. The three MSBs of the address are set to 111 and the

two MSBs are set to 10, to give an address 111xx10. Bits A2 and

A3 are determined by the state of the ADR pin. There are four

different configurations available on the ADR pin which

are explained in Table 4 below. This scheme allows four

ADR Configuration

Address

Low state

0xE4

Resistor to GND

0xEC

Floating (unconnected)

0xF4

High state

0xFC

Figure 6 and Figure 7 show timing diagrams for general read

specific conditions for different types of read and write

operates as follows:

1.

The master initiates data transfer by establishing a START

condition, defined as a high to low transition on the serial

data line SDA while the serial clock line SCL remains

high. This indicates that a data stream will follow. All slave

peripherals connected to the serial bus respond to the

START condition, and shift in the next 8 bits, consisting

of a 7-bit slave address (MSB first) plus a R/W bit, which

determines the direction of the data transfer, i.e. whether

data will be written to or read from the slave device (0 =

write, 1 = read).

The peripheral whose address corresponds to the

transmitted address responds by pulling the data line low

during the low period before the ninth clock pulse, known

as the acknowledge bit, and holding it low during the high

period of this clock pulse. All other devices on the bus

now remain idle while the selected device waits for data to

be read from or written to it. If the R/W bit is a 0, the

master will write to the slave device. If the R/W bit is a 1,

the master will read from the slave device.

2.

Data is sent over the serial bus in sequences of nine clock

pulses, eight bits of data followed by an acknowledge bit

from the slave device. Data transitions on the data line

must occur during the low period of the clock signal and

remain stable during the high period, as a low to high

transition when the clock is high may be interpreted as a

STOP signal.

If the operation is a write operation, the first data byte

after the slave address is a command byte. This tells the

slave device what to expect next. It may be an instruction

such as telling the slave device to expect a block write, or

it may simply be a register address that tells the slave

where subsequent data is to be written.

Since data can flow in only one direction as defined by the

R/W bit, it is not possible to send a command to a slave

device during a read operation. Before doing a read

operation, it may first be necessary to do a write operation

to tell the slave what sort of read operation to expect

and/or the address from which data is to be read.

3.

When all data bytes have been read or written, stop

conditions are established. In WRITE mode, the master

assert a STOP condition. In READ mode, the master

device will release the SDA line during the low period

before the ninth clock pulse, but the slave device will not

pull it low. This is known as No Acknowledge. The master

will then take the data line low during the low period

pulse to assert a STOP condition.