ADM9240 View Datasheet(PDF) - ON Semiconductor

Part Name

Description

Manufacturer

ADM9240

Low Cost Microprocessor System Hardware Monitor

ON Semiconductor 

ADM9240

When reading data from a register there are two possibilities:

1. If the ADM9240’s Address Pointer Register value is un-

known or not the desired value, it is first necessary to set it to

the correct value before data can be read from the desired

data register. This is done by performing a write to the

ADM9240 as before, but only the data byte containing the

register address is sent, as data is not to be written to the

register. This is shown in Figure 2b.

A read operation is then performed consisting of the serial

bus address, R/W bit set to 1, followed by the data byte read

from the data register. This is shown in Figure 2c.

2. If the Address Pointer Register is known to be already at the

desired address, data can be read from the corresponding

data register without first writing to the Address Pointer

Register, so Figure 2b can be omitted.

Notes:

1. Although it is possible to read a data byte from a data register

without first writing to the Address Pointer Register, if the

Address Pointer Register is already at the correct value, it is

not possible to write data to a register without writing to the

Address Pointer Register, because the first data byte of a

write is always written to the Address Pointer Register.

2. In Figures 2a to 2c, the serial bus address is shown as the

default value 01011(A1)(A0), where A1 and A0 are

hardwired to either Logic 0 or Logic 1.

ANALOG INPUTS

The ADM9240 has six analog inputs. Four of these are dedi-

cated to monitoring the following power supply voltages: +12 V,

+5 V, +3.3 V, +2.5 V.

These inputs are multiplexed into the on-chip, successive ap-

proximation, analog-to-digital converter. This has a resolution

of ten bits, but only eight bits are used for the voltage measure-

ment and limit comparison. The basic input range of the ADC

is 0 V to 2.5 V, and the power supply inputs are scaled by on-

chip attenuators such that the ADC produces an output of 3/4 ×

full scale or 192 decimal, when the input voltage is at its nomi-

nal value. The use of on-chip scaling guarantees accuracy and

removes the need for precision external resistors.

1

9

1

9

SCL

SDA

0

START BY

MASTER

1

0

1

1 A1 A0 R/ W

D7 D6 D5 D4 D3 D2 D1 D0

ACK. BY

ADM9240

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

Figure 2b. Writing to the Address Pointer Register only

ACK. BY STOP BY

ADM9240 MASTER

1

9

1

9

SCL

SDA

0

START BY

MASTER

bus address, R

1

0

1

1 A1 A0 R/ W

D7 D6 D5 D4 D3 D2 D1

FRAME 1

SERIAL BUS ADDRESS BYTE

ACK. BY

ADM9240

FRAME 2

DATA BYTE FROM ADM9240

Figure 2c. Reading Data from a Previously Selected Register

D0

NO ACK. STOP BY

BY MASTER MASTER

Rev. 2 | Page 8 of 22 | www.onsemi.com

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REV. 0

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